Lightweight battery replacement for GPS
It would depend on the power draw of your GPS equipment (are you using just a receiver or an entire computer system to analyze the data?) but lipo would be a good choice. A lipo can do high currents for long times without heating up, however it is not good with high heat environments.

You don't need a high C rate lipo, 20C at 5 or 10 amp hours will be plenty and much lighter.