Lead acid batteries used for automotive purpose are designed to provide high current for a very short duration (to start the vehicle). Automotive lead acid batteries are not designed to be regularly discharged by more than 25% of their rated capacity. The requirements of inverter systems are totally different. Inverters require “Deep Cycle” batteries to provide continuous power which can be discharged at least 50% of their rated capacity. Some good deep cycle batteries can be discharged over 70% of their capacity. Deep Cycle batteries have specially designed thick plates to withstand frequent charging and discharging.