For the Sprint, I use LiPo. I am still using some Spektrum RXer packs that are 4 years old. The Turbine battery is 3 years old now.

For the Flash, I use Spektrum LiPo Rxer Packs and Jetcat's LiFePo4. The Rxer packs are new this year. The Turbine battery is a couple years old.

I put them all in storage mode for the winter. Otherwise they are charged and ready to go all Spring, Summer and Fall. Once the Internal resistance starts showing up as going bad, then they get relegated to bench only use or disposed of. A good indicatorof the IR going whacky is when they timeout on the charger. Then it is time to get the IR meter out and see what is going on.