[drknapp]

I think you have a good idea.

Sounds like you are setting up a circuit similar to the Uninterruptable power supply in our computer room at work. Ours does charge the batteries while inverting. In our case this arrangement provides continous power in case of outages and also provides noise and voltage spike immunity for the equipment. There is also a circuit that bypasses the charger/inverter circuitry so that you can work on the system while providing power to the circuits.

I'm not an expert, but I think that the biggest thing you will have to watch for is to make sure that if you switch to "house" power you do break the circuit. You don't hit anything out of phase (if there are any motors on the circuits) as the inverter won't be synchronized to your house power.