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.