Battery Chargers or converters are often found in RV and off-grid applications. These units will charge your battery when connected to shore power or generator power.
RVer On The Road Tip
An easy way to test a battery charger in an RV when camping, is to unplug the RV from shore power and turn on the 12-volt lighting. Then plug the camper in, if the lights get brighter the converter is most likely working properly.