18kPV will charge LifePower4 batteries but will not pull from them.

I installed an 18kPV invertor and have 6 Lifepower4 batteries hooked up to the inverter. Firmware for the batteries are current.

The  inverter charges the batteries from both the grid and PV but when I disconnect the PV and grid power, the inverter does not fall back to the batteries. I just lose power in the house. Why is the inverter not pulling from the batteries when the grid and PV are disconnected?

Thanks!