I have a Schumacher WM-2500A automatic battery charger that is reading incorrect battery voltage. When connected to the battery and plugged in the charger runs a test mode to check battery quality,and charge status. I am unsure of the specific voltages the charger starts and stops charging, however I know that a standard car battery is considered fully charged at around 13.5 v. my problem is the charger is reading the battery voltage at around 1.5 - 2 volts higher than the actual battery voltage. Assuming the charger is calibrated to stop charging at 13.5 v, if I were to connect a battery with standing volts at 11.5 - 12v the charger sees the battery @ fully charged and shuts off. I have opened the case and looked for any kind of adjustment to calibrate the input voltage with no success. The charger worked fine when new,and is out of warranty so thats out. I paid almost $100.00 for the charger, and only used it occasionally, When connected to a very low(say 10 v) the charger will come on and charge but,will shut off at what it thinks is 13.5v, leaving me a partial charge. Any advice?