48 volt won't charge

Put power drive charger on new to me '96 48 volt DS. The plug inserted and removes very easily. The charger does not respond immediately but about 20 seconds later the charger clicks, the meter jumps to 15 then immediately goes back to 0. Left plugged in it does this about 4 or 5 tomes then nothing. No noises, no fan no nothing..... Am I doing something wrong? Should the plug fit tighter? The batteries have a charge. Need some direction here.
I am 1500 miles from home and most of my tools also. Any suggestions?????