I have a Xantrex model 300 powerpack, serial #B10780939. The battery test button says the battery is empty. When I plug the a/c charger in the battery status button flashes red then green and keeps repeating. The unit has not been charged for some time. I have a 1-amp a/c charger unit available, can I plug this charger into the battery 12 volt DC socket (Cigarette lighter style plug)?. Thanks, --charles--