I talked to Polk's about using a LiPo battery for the Tracker III transmitter and they advised against it due to the higher voltage. I switched the NiCd battery ti NiMh but the standard NiMh batteries self discharge at a high rate. I've since switched to using Sanyo's Eneloop NiMh batteries. They will hold 80% of their capacity for 6 months. In the last Model Aviation magazine (Sept '11) Red Scholefield, who writes the Battery Clinic section, says he's been using the Eneloops for over 2 years and when he checked the batteries they had not lost any of their original capacity. I'm using the Eneloops in all my transmitters and as reciever flight pack batteries. In my Tracker III and my Hitec Eclipse I'm using an 8 cell battery holder, and 4 cell battery holders for the flight packs. You can get Eneloops with solder tabs from Batteries America (
www.batteriesamerica.com) or Battery Space (
www.batteryspace.com) costs $0.25 per cell for tabs. Battery Space also has the best selection of battery holders.
To use a LiPo for a reciever battery you need a voltage regulator to drop the voltage to 5 or 6 volts from a 2 cell 7.4 volt pack otherwise you'll burn out your reciever or servos.