Neal,

I think there are still a lot of pilot using Sealed Lead Acid (SLA) batteries in their glider. It works OK for gliders that maybe have an electronic Vario and a radio.

As you add other electric devices, especially a transponder, the capacity demands go up. You can get SLA batteries with 12-15AH capacity, but many ships are equipped with Lithium/Iron/Phosphate (LiFePo) chemistry batteries.

Most of the sailplane accessory distributors have them in stock, for example:

http://craggyaero.com/lifepo4_battery1.htm

Hope that helps,

Mike