If you can assess the cells where you fill with water and if you have a volt meter connect your meter leads to shot pisces of wire to be thrown away later. Put the positive lead on the positive post of the battery. Put the wire connected to the negative lead in the water of the first cell nearest the positive post. On a twelve volt battery there your meter should show 2 volts. Each cell can be tested individually with this method. Just work your way from positive to negative until you reach the Negative post moving both leads as you go. Don't let your wires touch the plates in the battery Just dip the wires in the battery acid a little bit. Thats all you need for a reading. If you find a cell that has less than 2 volts you have found a dead cell and that would cause your problem. + OOO OOO - Batt 1_1 __ 22 ____3 3 ______4 4 ________55 _________6_6 It takes six readings like that. I didn't no how else to show this. I hope I explained it OK.I repeat don't stick the wires in too far. Hope this helps. PS this works best after charging the Battery. A dead cell wont accept a charge.