This power stage is unique to the storage ready inverters. It works as a battery charger in one direction and as a constant voltage DC/DC converter to convert the variable battery voltage to the required constant bus voltage level in the other direction. Though Lead-acid type batteries are very popular in energy storage systems, newer systems are increasingly moving to various types of Lithium batteries. The battery voltage depends upon the system power level. Lower power single phase systems commonly use 48-V battery, while higher power three phase systems use 400-V battery. Intermediate battery voltages are used infrequently. Systems with higher power range of string inverters could use 800-V battery for storage.

The common topologies for the bidirectional DC/DC power stage are the CLLLC converter and the Dual Active Bridge (DAB) in isolated configuration. In non-isolated configurations, the synchronous boost converter can be used as a bidirectional power stage. In low cost single phase systems with lower battery voltages, current-fed push-pull topology (with or without active clamp) is also used.