Have you turned it on? The inverter can draw down the batteries severely if the outlets it powers are used inadvertently, so you have to turn it on via a switch in the kitchen, then plug in each device you want to use in an outlet marked Inverter. Only the furnace and overhead lights will draw from the batteries directly, and those will use AC current first if it is available.
A flat screen TV doesn't draw a lot of current, but a toaster, hairdryer or other heat producing appliance will quickly deplete batteries.
I believe having the battery switch in STORE mode would also disable the inverter.
Today is a gift, that's why they call it the present.