TXT dead battery problem

[norbon]

I put my TXT cart up for the winter fully charged and now it won't run and the charger shows low battery voltage and will not charge. I tried charging each battery by itself and 3 took a charge and 3 would not. If I read the voltage across the entire bank I get 16.5 v and across the 3 charged ones I get the 16.5v. This battery bank is only one season old and are Trogans. The bad batteries read 0.00 to .03 v. What could make half of the bank die ? Any help would be appreciated. I really don't want to buy more batteries. Thanks, Norbon