If it's a Nicad like mine:

I can discharge the Rx 600mA battery completely through my Hobbico tester. It's a voltmeter that simulated the load of the Rx system. The Tx, you can just leave on.
I used to discharge it through an 12V automotive bulb or a large 5W resistor, something around 20 ohm to give me about a 250mA dicharge rate.
Once completely discharged, make sure you charge it again completely and uninterrupted. This's called cycling the battery. You can also buy charges to do the same thing. This every once in awhile erases or reduces the "memory" of the battery.


I don't like to discharge the Rx battery in the plane, because once the battery gets below a certain point, the electronics go nuts and jack the servos hard to one side.

I don't know about the Li-polymer stuff.