Getting energy into the battery is only part of the BESS challenge. The system is designed to transfer the electrical energy stored in the battery to the load, which typically requires a 120/240VAC line to power devices and systems.

The output function requires a DC/AC inverter that converts the battery's DC output to line-compatible AC. Like the electronics between the power supply and the battery, the inverter is not a "one size fits all" unit. Engineers must consider the topology and design of the inverter, along with many design challenges and trade-offs. Although there is no formal definition, experts often divide inverters into three power and characteristic categories: low power, medium power, and high power.