NiMh and NiCd voltages change very little from 90% charge to 5% charge. The change is smaller than the difference between a new and used NiMh. The change is smaller than a cold and hot NiMh. The change is even smaller than the voltage drop across a slightly dirty battery contact. Because of all these reasons, there is no way of measuring the battery voltage and determining the remaining charge. The LED's are not a good indicator of the battery life of a NiMh. A fully charged battery can indicate red and a nearly discharged battery can indicate green, though that's rare. What the LED's can tell you is when the LEDs are off, the battery is dead.
If the battery has the capacity to hold a full charge, then the timer is dependable. A good AA NiMh will run an SM at 100 mW for 4 hours. When the timer reaches 3 hours, it is probably time to start thinking of replacing the battery. If you must have battery life readouts and the timer is not satisfactory, then alkaline or lithium disposable batteries are your choice. You can test batteries in the transmitters by letting them run down and stop the receiver timer. This will give you a good idea of what your particular brand of batteries can do. If a battery is low capacity, discard it. It's not worth the danger of accidentally ending up in a high value situation.
An HM plug on transmitter was tested with three types of AA batteries. Alkaline batteries ran for 5 hours with a dynamic mic plugged on. Alkaline batteries lasted for 3.5 hours with a Sanken CS1 plugged on with the HM providing the 48 Volt phantom power. New Sanyo rechargeable NiMh batteries, measured at 2500 mAh capacity, ran the HM for 9.25 hours with the dynamic and 7 hours with the CS1. Lithium Eveready AA's were outstanding at 16 hours with the dynamic mic and 12.75 hours with the CS1. Your mileage may vary and in the case of the alkalines, will depend on temperature.
Here's a reply to a customer who had an SMd that would only run for 6 hours on lithium batteries.
There have been four problems with the SMd battery setup. Here's the problems:
All of these are considered to be our design fault and come under the extended "we blew it" warranty and will be fixed at no charge or automatically upgraded if a unit comes in for other things. Also, these fixes have been in the units for some time. However, not all were done at once since we didn't find them all at once and they didn't fail on most units.
As far as battery life, the lower capacity "Advanced" lithium batteries run an SMd for 12.7 hours. We will have the "Ultimate" lithium numbers in a day or so but they should be around the 15 hour number.
The early iPower batteries were larger than a standard 9 Volt battery. Shortly after their initial release they made a smaller case for the batteries.
The new smaller 500 mAh units are marked the same as the older, larger 500 mAh units. The only difference I see in the case is that the older unit has a small recessed circular area only around the small positive terminal. The new smaller 500 mAh unit has a large rectangular recessed area that encloses almost the entire top of the battery. It's recessed about 0.030" deep. The new batteries are actually smaller than standard 9 Volts and should never be a problem as far as sticking.
We were told in early 2006 that it would be several weeks before the first new batteries were available. We only stock the smaller cells because we don't want them stuck in our units. If you order from some one else, I think I'd do it verbally to confirm what you want. If you have some of the larger batteries you might contact iPower and see if you can return them. Do a search on the RAMPS newsgroup for contact information.
Alkaline batteries, though very good at room temperature, cannot deliver much current at lower temperatures. Battery life can be as little as one third normal on a cold day and even less if they cold soak for any length of time. Life can be as little as just a few minutes at -20 F.
If you must use disposable batteries (non rechargeable) then lithium batteries are the only good choice. They have shorter life at low temperatures but are still much better than alkalines.
In the AA battery size, lithium and NiMh batteries are the best cold weather choice. At low temperatures NiMh have almost as much life as at room temperature and are rechargeable to boot. Our tests indicate that the NiMh AA batteries when used in an MM400 or SM transmitter have 75% of normal capacity at minus 15C (-15C) or +5F. We recommend the Eveready NiMh batteries and 15 minute charger that we provide with the SM, SMD and SMQ transmitters. One precaution is that the batteries cannot be recharged if they are cold. They can be used cold without any problem but must be at about room temperature to be recharged. The lithium batteries are also good at low temperatures but they don't like being cold for long periods of time. If cold soaked at 5 deg F for an hour, they still have 95% of their normal capacity. Allowed to cold soak overnight they only have 50% of their capacity. Here are some run times in a cold SM transmitter at different temperatures:
At room temperature:
At 5 def F cold soaked for one hour:
At 5 deg F cold soaked for 16 hours:
In the 9 Volt battery size, NiMh batteries perform as well cold as they do at room temperature but they don't have much battery life (capacity) cold or warm. At one time they were the only choice for very low temperatures but LiPoly rechargeable batteries are now available that have more capacity than alkaline batteries and perform very well at low temperature. They are currently sold under the iPower brand and are available on the internet, from some dealers and from Lectrosonics. (See FAQ#086-WIRELESS)
Here's a long post that appeared on the news group RAMPS. What is RAMPS? (See FAQ021-WIRELESS)
To the Group:
Here's the results of the new version of the iPower 500 mA rechargeable Li Ion Polymer battery tests. We also ran tests on the Ultralife 9 Volt single use lithiums and standard Eveready alkaline 9 Volts for reference. The batteries were run down multiple times in a UM450 because it is a power hog, 125 mA at 8 Volts or 1 Watt (!). We then ran the batteries down in a UM400 (a power piglet) just for further reference. In all cases the transmitters were run continuously until shut down of the transmitter. The batteries were then put on the charger and recharged. It made little difference if the battery was charged for one hour (green indicator just came on) or overnight. The runs were at 72 F ambient. Here's the results:
The first iPower battery in UM450:
The second iPower battery in UM450:
3:10 (double charged. See end of post.)
Brand new from the factory Ultralife Lithium in UM450:
Few months old Eveready Alkaline in UM450:
The Ultralife does not like the high current demands of the UM450 and does worse than an Eveready alkaline. The 500 mAh iPower has almost exactly 50% more capacity than either, at this high current load. If you remember the previously posted cold tests, the iPower also did quite well, though that was on a 400 mAh battery. Below are tests in a UM400, a more normal load:
The first iPower battery in UM400:
The second iPower battery in UM400:
Two brand new from the factory Ultralife Lithiums in UM400:
Two (few months old) Eveready Alkalines in UM400:
Here the Ultralife Lithiums come into their own, since the current drains are more reasonable and show a 62% increase in battery life compared to the Eveready alkalines as standards. The iPowers still show a good 20% increase over the alkalines.
This UM400 was a block 29 and seemed to pull a little more current than the average UM400. The ratios of battery life should still be valid. If you are getting a particular battery life on alkaline Evereadys, simply add the proper percentage. If you are using ProCells (Mallory) the iPower improvement will be an additional 10% more (30% instead of 20% for example).
Doing a 100% discharge on Li Ion Poly batteries (iPowers) is worst case for usage.
The iPowers work well in the cold.
We tried a "double" charge on the iPower with no big effect. We charged it completely, removed the battery, and started the charge cycle again. It took about an hour for the charging light to go from red to green again. I don't know what that means, but it didn't look good. However, the capacity of the battery went down only 4 minutes. I don't think it was significant, but....
We will ship the iPower system with the UM450.
I can't stress enough that "YMMV".
All rechargeable batteries wear out. Your car battery is a well known example. Every time a rechargeable battery is used, it loses a small amount of capacity. Whether that becomes a problem or not depends on how much capacity you need. Here's an example: let's say you have an SM transmitter and the NiMh AA rechargeable batteries that we provide, currently 4 each 2200mAh Eveready batteries. These batteries happen to run your SM transmitter for 4 hours and 5 minutes (4:05) and that is just fine with you because you only have to operate the transmitter for exactly four hours every day. In few weeks, you are going to be very disappointed, because after 20 charges, the battery will only power the transmitter for 3:59. The reason is that every time you charge the batteries you will lose a tiny amount of capacity and you don't have any spare capacity to lose. In fact after a year of use, the batteries will probably only run the transmitter for 3 hours. There is nothing wrong with the batteries or the transmitter. Rechargeable batteries just slowly wear out.
The solution is to start out with a higher capacity NiMh AA battery such as an Eveready 2500 mAh cell or a Sanyo 2700 mAh cell. You will now get almost 5 hours of battery life initially and you won't be down to 4 hours of life until 200 recharges or 6 months later. This is even after assuming that the higher capacity batteries wear out twice as fast. (Eveready quotes the 2200 mAh battery as being rechargeable 1000 times and the 2500 mAh being rechargeable 500 times.)
This is an extreme example caused by your run time requirements being so close to the limits of the smaller capacity battery. If you only needed 2 hours of battery operating time, the smaller battery would be fine and would actually operate for many years before falling below your requirements. If you look at the economics of the battery for the SM, the rechargeable batteries really make sense. Top quality alkaline batteries will only run the SM transmitter for less than two hours and cost about 40 cents apiece. Two hours is rarely long enough. Lithium AA batteries will run the SM for 6 hours but they are $2.00 each. High capacity NiMh AA batteries are $3.00 each but the cost per use is a tiny 1.5 cents. Compared to a lithium AA battery, just two uses of a rechargeable AA pays for the battery.
This discussion is also applicable to the iPower 9 Volt lithium ion polymer rechargeable battery. Exactly the same arguments can be made about both saving money and gradual wear out of the battery with recharging. (See FAQ#089-WIRELESS)
Q: So do rechargeable batteries wear out?
Q: How many times can I recharge them?
A: It depends on your run time requirements.
Q: How do i know when they are worn out?
A: When they no longer meet your requirements.
Here is a memo we sent to our dealers and service people about batteries. Please realize it is therefore a little blunter than our usual FAQ's:
If you are using alkaline batteries, we recommend the use of Eveready alkaline batteries particularly in our synthesized (frequency agile) equipment. Other brand batteries may work perfectly well, but Eveready is our standard for testing and analysis. In different purchases of Duracell batteries from different locations, we have found the battery life to vary by more than 2 to 1. On the other hand, we have found very consistent results from Eveready batteries. Also, in all tests we have done, a standard Eveready Energizer always gives us longer battery life than standard Duracell Procells. If customers call complaining of battery life we should ask them to try an Eveready Energizer before returning equipment for repair. Assure our customer that this does not mean Duracell is a bad battery , but that the Duracell battery was not intended or designed for the heavy current draw our equipment requires.
Always try to get the customer to try the Eveready batteries. If it is necessary to convince the customer to try Eveready's in a test, we can send them free batteries. That is cheaper than us wasting our time and theirs testing a perfectly good unit and finding no problem. Try to talk to the actual user of the Lectro product rather than someone who has been tasked with returning the unit and has no idea of what is going on. Remember these points.
We have had 3 Venue systems in the field that either don't want to power up or if they do power up, run for a few seconds to several hours and then shut down. Since replacing the external power supply with a different type "fixed" the problem, we suspected the external power supply. However, we were never able to get a "bad" supply" to fail. We overloaded them by 50% and heated them to 150 degrees F ambient and they merrily continued working. The answer turned out to be much simpler than the maligned power supplies.
On Venues with a full compliment (six) of the new VRS or VRT modules, the electrical current requirements are too close to the electrical current rating of the input fuse on the main board (VRM). This is currently a 1.5 Amp polyfuse. A fully loaded Venue with the newest mainframe and newest modules pulls 16.7 Watts. This is 1.4 Amps at 12 Volts or 1.1 Amps at 15 Volts. Both these number are getting too close to what the polyfuse is guaranteed to handle, particularly at higher temperatures. We have 2.5 Amp fuses in stock that are exactly the same physical size as the 1.5 Amp fuse. We changed out all the 1.5 Amp fuse in units at Lectro and are using the 2.5 Amp fuse in all future units. We will send free fuses to customers upon request (800 821-1121 or
The polyfuse is under the main cover and is about 1 inch away from the red power switch on the front panel. We have put pictures and instructions on our web site. Here's a link: Venue polyfuse. Two soldering iron tips heating the opposite pads of the polyfuse will remove it in seconds. If you screw it up, we'll still fix it at no charge.
The standard external power supply (DCR15/1A2U) for the Venue is an 18+ Watt unit and is OK to run the new Venues. The maximum power the Venue pulls with six VRS's or VRT's is 16.5 Watts. In testing, we have overloaded the standard Venue power supply to 25 Watts for 2 hours and it was fine. We will load the supply to even higher levels and also run it at high loads in the oven to just be sure that it isn't a part of the problem. (The tests after this was first written show the supply delivering 37 Watts at room temperature and 24 Watts at both 150 degrees F. and at 90 Volts line voltage input.)
This fuse overload would explain why checking the external supply always shows the supply to be good. The reason substitute supplies "fixed" the problem is that if a substitute supply has slightly higher voltage under load, the current demand from the Venue will be less and the fuse would then be OK. Remember, the fuse is right on the edge of working or not.
Since this was posted on 2006-03-02, we have come up with a third solution for interrupting the ground loop. See Isolating Battery Eliminator
What's happening is that the switching power supplies inside the UM400 transmitters create noise on the ground plane. This noise then has two paths because of the dual ground paths: one through the DC power and one through the audio ground connected by the mixer. Although mixers often have a transformer balanced output, some transformers have capacitance which can couple pins 1 and 2 to ground at high frequencies (such as hiss from DC switching supplies).
The solutions to this are as follows:
An Eveready brand alkaline battery will power the LM for a little over 6 hours at room temperature. This time is from turn on until the transmitter shuts off. Lower temperatures, stale batteries or different brands will affect the operating time.
The times given are for turn on till shutdown (failure) of the respective transmitter. Times on alkaline AA's will drop greatly if the batteries are below room temperature. These times are typical and not guaranteed. Also note that the batteries were fresh and in excellent shape.
The SM or MM transmitter will operate for slightly less than 2 hours on one Eveready or Panasonic alkaline AA battery, for 4 hours and 5 minutes on an Eveready 2200 mAh NiMh battery and for 6 hours and 30 minutes on an Eveready lithium battery.
The SMd dual battery 100 mW transmitter will operate for slightly less than 6 hours on two Eveready or Panasonic alkaline AA batteries, for 8 hours and 30 minutes on two Eveready 2200 mAh NiMh batteries and for more than 14 hours on two Eveready lithium batteries.
The SMq dual battery 250 mW transmitter will operate for slightly less than 2 hours on two Eveready or Panasonic alkaline AA batteries, for 5 hours on two Eveready 2200 mAh NiMh batteries and for 7 1/2 hour on two Eveready lithiums.
The variable power SMv transmitter will operate at 50 mW for 2 hours on an alkaline AA, for 4:45 on a 2200mAh NiMh AA, and for 7:20 on an Eveready lithium AA.
The variable power SMqv dual battery transmitter will operate at 50 mW for 5:50 hours on two alkaline AA's, for 9 hours on two 2200mAh NiMh AA's, and for 14:40 on two Eveready lithium AA's.
Your mileage may vary, See FAQ#087-WIRELESS.
The original reply made 13 Jun 05 is below. It is long but does discuss why the problem exists. In short, the problem is due to a ground loop between the common ground between the audio cable shield, the power supply cable to the transmitter and the power supply ground to the mixer. On 15 Nov 06 we released a new product which solves the problem by isolating the ground to the transmitter. ISO9VOLT battery eliminator
This was an email from a customer:
We are unable to use the Lectrosonic 400 series wireless mics as camera links between our mixers and the Panasonic Varicams. While the units work fine between talent and mixer, there is a significant signal to noise problem when used from the mixer to the cameras. We have traced the problem to the use of the external power modules for the transmitters and/or the battery distribution box (Hawk Woods) we are using. Comparison with a 400 transmitter powered by a disposable 9 volt battery demonstrates the desired performance.
(Lectrosonic makes a unit called the battery eliminator which allows their transmitters to be externally powered and therefore eliminates the accidental loss of audio between mixer and camera due to an undetected battery run down. Our sound packages, mixer, receivers and transmitters are powered from a rechargeable NP 13 battery via a power distribution tap made by Hawk Woods with a variety of cables [4 pin to single and dual coaxial ] and the aforementioned battery eliminators.)
This s/n hiss is introduced at the transmitter and is related to a ground potential between the 400 transmitters and any other ground in the package. Dc voltage from 411 transmitters to ground of mixer measures 4.5mV. Resistance, which should be 0, measures 4 or 5 ohms. This results in audible hiss between our mixers and the cameras. Changing the power cables, audio cables or battery eliminators does not solve the problem. The more equipment added to the Hawk Woods power distribution, the louder the hiss becomes.
This is the same power scheme we have used with the rented Lectrosonic 200 series transmitters without any problem. We are shocked that this problem is unknown by Lectro and the wider sound community.
Our First reply:
The hiss problem is probably caused by a ground loop between the common battery feed to the mixer and transmitter and the audio ground to the transmitter. The switching power supply in the UM400 is noisier than the linear regulator in the UM200. This is invariably true of switching power supplies and is a trade off for their greatly improved efficiency. The reason the ground loop problem is showing up on the transmitter is that this is probably the lowest level audio in the system. When the UM400 is run from a 9 Volt internal battery, the ground loop is broken and every thing is normal.
One solution would be to star ground every thing with separate lines at the transmitter input since it is the most sensitive point in the system. The other would be to use an isolation transformer in the audio feed to the transmitter. Neither of these is very easy. The easiest solution is to use the balanced output of the 442 mixer to accomplish the same thing.
The balanced input would be wired so that pin 1 of the 442 output XLR goes to the cable shield and pin 1 of the UM400. Pin 2 of the XLR goes to pin 5 of the transmitter (line level input). Pin 4 of the UM400 goes to pin 1 of UM400 to form the line level pad. Then pin 3 of the 442 XLR goes to pin 1 of the UM400 (along with the shield of the cable). This way the balanced output of the 442 is referenced to pin 1 (local ground) of the transmitter. This will require a 2 conductor plus shield cable of course.
We will duplicate the problem here if possible with our 442 mixer and then apply the "cure". We should get this done in the next few days and will let you know how well it works.
One other thing that could be adding to the noise problem is if the UM400 is not receiving a line level signal. If the output from the mixer is fed directly to pin three of the UM400, the sensitivity to ground loop noise will be 20 dB worse than if the signal is fed at line level to pin 5 with pin 4 tied to pin 1.
The battery drain increases by a third if you use a high current mic at 48 Volts. Fortunately, the most common professional mics are relatively low current (such as Sennheisers). Approximate battery life will go from 4.5 hours at no phantom, to 3.7 hours with a low current mic, and to 3 hours with a high current mic. Battery life can be improved for some low voltage, high current Schoeps by running them in the 18 Volt position. A number of popular performing microphones are just as happy at 11 Volts as they are at 48 Volts. There is absolutely no advantage to running them at 48 Volts; it is just wasted battery power. Switch the UH transmitter to 18 Volts with these mics and reduction in battery life will be reduced by more than half.
So the overall answer here is, check the specs of the microphone to see what minimum voltage it really requires and then set the UH to 18 Volts if possible. If you do that you should lose even less than a half hour of battery life. If the specs are not at hand, try running the mic at 18 Volts and see if you are happy with the results. In fact, have someone else switch the voltage and see if you can tell the difference, no matter what the specs say. You may be able to save some battery money.
Yes and no. If you charge the battery just until the charger indicates that it is done with the fast charge, you will have charged for 15 minutes or less. A reasonable person that hadn't read the manual, (like you and me), would think that it is completely done. In fact, it is only changing from the high charge rate to a trickle charge. If you stop charging at this point, you will get about 90% of full performance out of the battery. If that is all you need, then there is no reason not to just do a 15 minute charge. To get the last bit of charge into the battery, however, you will have to let it remain on the charger for another hour or a little more. It is still pretty remarkable that you can get a nearly fully charged battery in only 15 minutes.
The reason for the slight undercharge is that the battery gets hot from having charge crammed into it in such a short period of time. The charging current is over 8 Amps. That's why the 15 minute chargers actually blow cooling air over the battery and the charger's electronics.
Hot NiMh batteries do not hold as much charge as a room temperature battery. So it is necessary to allow the battery to cool down a bit before the last bit of charge can be put into the battery using a trickle charge of a fraction of an Amp.
UCR201 receivers built between the beginning of 2004 and January of 2005 have a voltage divider problem that we became aware of in early February of 2005. External supply voltages greater than 12 Volts overload the analog inputs of the microprocessor and cause all analog readings such as audio level and RF level to be incorrect. This also causes the scan function to work incorrectly and display "interference" in frequency bands where there actually is no interference.
The quick solution is to run the 201 from 9 Volt batteries or power it from voltages below 12 Volts. The permanent and better solution is to let us modify the unit at no charge, in or out of warranty. This can be done by us at the factory, by one of our servicing dealers or by you if you are moderately handy with a soldering pencil. We will send the surface mount diode, layout drawing and "fix it" instructions to anyone who needs the fix. Check with service to get the package. We include an extra diode because if you drop one on the rug, you'll never find it.
All units shipped after 9 Feb 2005 will have the same fix as described below and the next board rev will incorporate the exact same fix. The fix consists of a small SOT23 surface mount diode from the offending voltage divider to the 5 Volt supply at the micro-processor. The 3 terminal diode is soldered to a copper trace and to two vias on the board. It is necessary to scrape a little bit of solder mask (green screen) from the trace so the solder can bond. This fix, or attempt at a fix, does not affect the warranty. Using a Black Beauty soldering iron and blow torch will, however, result in nasty comments from the repair crew.
The following units were in our finished gods and have been modified already:
5269, 5304, 5321, 5389-5394, 5417-5419, 5458-5459, 5463, 5465-5469, 5471-5479, 5484-5504, 5508-5515, 5517. Dashes indicate anything between these number are OK.
Another rule of thumb. Anything shipped from Lectro after 9 Feb 05 is modified and any units in for repair after that date will be modified.
If you are using alkaline batteries, you will have very short battery life. The MM400 and the SM transmitters use a single AA battery to reduce size and weight. Since they are 100 mW transmitters, the load on the single battery is unusually high, about 450 mAh. Alkaline batteries are not designed for that high a current and will last less than 2 hours at room temperature. In cold weather, the run time is much less and can be on the order of minutes.
Lithium batteries can provide higher currents and will run slightly more than 6 hours at room temperature. If run a few hours at a time, they can provide a maximum of 8 hours of life. However at freezing temperatures they have shorter run times. (See FAQ I don't get much battery life in my transmitters when they are cold. What kind of batteries should I be using this winter?)
NiMh batteries are now available with capacity ratings of 2500 mAh and will operate the MM400 or SM transmitters for slightly over 4 hours. The above times were made with very fresh batteries; as the ads say "Your mileage may vary".
With 15 minute chargers available from several large and reliable battery manufacturers, they are a very viable alternative. Some of these chargers (RayOVac and Eveready) will operate from a 12 VDC source. Finally, the NiMh batteries are not nearly as sensitive to low temperatures as other battery types.
There are three possibilities: One, batteries do not like to be cold. At low temperatures (32F) battery life can be one third of that at room temperature (72F). Two, some brands of batteries will not deliver the high currents used in our receivers and 100 mW transmitters. We use Eveready as our standard battery. Three, our units will operate to very low battery voltages and you may not be running the battery down far enough. Here's a reply to a UCR201 user that was replacing batteries every 2 hours or so.
At room temperature, the 201 should give you +4 hours of operation. Try an experiment when you have some free time with a fresh battery. Simply run the unit in the battery voltage display mode and see how long it takes to pull the battery down to 6.5 Volts. The system will operate perfectly to below 6.5 Volts since all internal voltages come from several switching power supplies. We have found a lot of variation in XXXX batteries and some batches will not provide the high currents the 201 draws. We have never found problems with Eveready 9 Volts. The XXXX batteries acted so weird I suspected they might be counterfeit. This was on several batches of XXXXXs from different parts of the country. Further testing found that other XXXXXs were almost equivalent to the Eveready's. We remain puzzled. My advice is that if you are getting short life, try the Eveready's as a standard before deciding the unit is defective.
If you are having short battery life in transmitters due to cold weather, keep the transmitter warm as long as possible before you have to use it. Belt pack transmitters can be also be put under the coat so as to be next to the nice warm human being.Alkaline batteries, though very good at room temperature, cannot deliver much current at lower temperatures. Battery life can be as little as one third normal on a cold day and even less if they cold soak for any length of time. Life can be as little as just a few minutes at -20 F.
If you must use disposable batteries (non rechargeable) then lithium batteries are the only good choice. They have shorter life at low temperatures but are still much better than alkalines.
In the AA battery size, NiMh batteries are a good cold weather choice. At low temperatures they have almost as much life as at room temperature and are rechargeable to boot. We recommend the Eveready NiMh batteries and 15 minute charger that we provide with the SM, SMD and SMQ transmitters. One precaution is that the batteries cannot be recharged if they are cold. They can be used without any problem but must be at about room temperature to be recharged. (See FAQ I don't get much battery life in my transmitters when they are cold. What kind of batteries should I be using this winter?)
In the 9 Volt battery size, NiMh batteries perform as well cold as they do at room temperature but they don't have much battery life (capacity) cold or warm. At one time they were the only choice for very low temperatures but LiPoly rechargeable batteries are now available that have more capacity than alkaline batteries and perform very well at low temperature. They are currently sold under the iPower brand and are available on the internet, from some dealers and from Lectrosonics.
Here's the answer I posted on RAMPS about 9 Volt battery life:
Here's the last of the 9 Volt battery tests. This is a similar test to what we did in a previous post but with a high power transmitter. (See also FAQ How long will different types of 9 Volt batteries operate my transmitter?) For newer tests on the iPower LiPoly rechargeable 9 Volt (See FAQ How do the rechargeable 9 Volt iPower batteries compare to other batteries? How long will they operate my unit?) Here is what we did this time: we used a 250mW transmitter, a Lectro UM250 in the testing. This is a 250 mW UHF belt pack transmitter that eats 9 Volts like they were potato chips. This particular unit pulled 105 mA. We ran three different kinds of batteries to a final voltage of both 7.0 and 6.6 Volts. 7.0 Volts is where the LED is pretty dim and where two of our receivers with battery readouts start indicating low battery and 6.6 Volts is the very low battery indication. The transmitter is getting close to completely dying at 6.6 Volts but will usually run to 6.4 Volts or less. The LED goes out totally at 6.8 Volts. I'll list the type of battery and then the very dim LED point (7.0 Volts) and then the maximum use (6.6 Volts). Your mileage may vary.
These are interesting results. If you saw the earlier post with a similar table, you will notice that the Ultra alkaline has the same 50% advantage to 7 Volts but when run to 6.6 Volts, has instead, a 13% LOSS. This is not the same as for a 100 mW transmitter. There the Ultra was 50% ahead at either end point voltage. The Ultra fell like a rock when the voltage got to 6.6 Volts. In fairness to the battery manufacturer, these 1/4 watt units are very hard on batteries. Same disclaimer as before: These were fresh, new batteries at room temperature. This was one test, performed on one transmitter. And same anti-disclaimer: Most brands of alkaline batteries are about the same, alkalines and lithiums have a long shelf life, and our transmitters are pretty consistent. In any case, the ratios of battery life should be good numbers. You guys and gals know what kind of battery life you are getting now, and the ratios should be informative. We have found Eveready to be the most consistent general purpose alkaline.
On to other projects. I've seen enough battery strip charts for a while.