Using an automotive battery charger when onboard fails

Lots of chargers get confused and shut off in constant voltage absorption when the load on battery changes like a fridge cycling off. I have a schumacher which would stay running but voltage would spike to 15.5v+ when compressor shut off and drop to 12.8v when it cycled back . This happenen on 12 amp setting. On two or 25 amp setting it would shut off.