Your Goal Zero Yeti uses custom designed Lithium Ion. Here are some basic facts about Lithium Ion batteries:
1. Lithium Ion batteries can store and release a lot of energy in a short period of time. The batteries in your Goal Zero Yeti are in a protective enclosure with a sophisticated battery management and protection system controlling its terminals to the outside world.
2. It is critical that your battery does not get wet as moisture and water can get into the battery cells behind the protection circuitry and bypass that protection.