ORIGINAL: da Rock
Going up to 1650mAh for your TX is easy. Going higher means you're going to have to deal with batteries that aren't as user friendly. And my 1100mAh TX batteries last me all day. And the TX voltage readout makes dealing with the TX batteries easy. NiMH work great in TXs.
Boy you have that right!
I left my NiMH 1400mAh equipped JR 8 channel TX on for over 12 hours by accident and it still could have let me fly for several hours.
ro347:
There are TONS of suitable batteries available, including those from the already mentioned sites and Tower and Horizon.
At worst purchase a suitable pack and solder on the connectors from your old pack.