I did a house today where the seller had a car battery charging through some kind of adapter from a 30 amp circuit. The intent was to have the battery ready to power an inverter for the sump pump if power went out. The inverter was not connected to the battery at the time. My question is, does this present enough of a backfeed situation in an outage to worry about? The adapter had warnings all over it, telling me to read the manual… wherever that is.