go to walmart, get a cigerette plug in battery tester, there by the battery's and cost 14.99, they show true voltage, and weather it is charging or not. I used mine to diagnose a bad regulator ( wasn't stopping charge ) because it was charging to 14.9 volts, and then the belt would squeal constantly on the alternator, changed the regulator and it charges to 14.5 volts and no problems.