12V 100Ah GEL Battery: To keep a GEL battery healthy and prevent it from dying early, you should only use 50% of its capacity. This gives you roughly 600Wh of usable energy.12.8V 50Ah LiFePO4 Battery: Lithium batteries can safely handle a 90-100% discharge. At 90% DoD, you get approximately 576Wh of usable energy.