I know that NiMH batteries self-discharge over time, but mine are discharging in just a matter of hours. I am using them in a RC airplane. They are 9.6V 650mah AAA packs. I charge them up just as they should be and they put out full power when I test them in my plane. I go to the gym for a couple hours and stop by the flying field on the way home, but when I plug the battery in the motor on the airplane immediately goes to cut-off.An interesting note: If I hold the arming button down to keep the motor going, eventually it will work itself up to putting out enough power to do some low powered flight and will last the duration over normal flight time for the airplane
The battery pack is new to you, but it could have been on the shelf in the store or a warehouse for a very long time, easily a couple of years. A single bad cell can ruin a battery pack. 1) One of the cells might have gone bad and can't hold much charge, so it depletes quickly during discharge. The available battery voltage then is 9.6 - 1.2 8.4 volts. As current flows through the bad cell the current reverse-charges the cell, and the available voltage drops to 8.4 - 1.2 7.2 volts. 2) When a motor starts it requires a high current, and this drops the voltage out of the battery due to the internal resistance of the battery. If one cell is bad then the internal resistance is very high. Once the motor is running the required current is less, so the internal resistance of the battery is less, and the battery is able to maintain an adequate voltage. Factories do not test the cells to match their discharge cycles. This can happen to any battery. Car batteries, sealed lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium batteries. extra : This is a huge problem for any large power-storage system, from solar-cell systems to hospitals and server farms. They use large battery banks to give them ride-over time until they can get their gasoline/diesel/natgas generators running. Monitoring each cell in a battery requires special electronics and in the past was not worth the trouble due to the cost. There are now electronic designs that will do this monitoring, but it's not going to be done for cheap RC battery packs.
one or more of the cells has failed leading other cells to discharge into it , buy some tagged AAA cells and rebuild the packs
