All inverter/chargers I've seen have an automatic transfer switch so that as soon as you connect to shore power (or start generator) the inverter is bypassed. At that point the charger section of the inverter/charger starts to charge the batteries.
I don't know whether the transfer switch would work or not if the inverter/charger goes out, but I assume that's a problem that can occur with a simple inverter also. Additionally, I think I may be able to bypass the entire unit by rewiring in an emergency if the wires are long enough.
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