I used this battery to replace the original 900 mah NiCad (yes that's correct - NiCad) in my Tracker III transmitter when it started self discharging very quickly after many years of use. It is a snug fit but no modification was necessary. With twice the capacity of the original battery and NO self discharge, I need charge only after four or five flying sessions and even then the voltage is still at the nominal 9.9.
Remember to set your charger for the LiFe 9.9 volts not the 11.1 volts of a LiPo. I also chose the LiFe battery rather than a LiPo since it is closer to the 9.6 volts of the original NiCad.