Beware trying to measure AC voltage across the battery when charging. My digital multimeter consistently gives a reading of about 30 volts AC! Both with the engine running (alternator charging) and with my CTEK battery charger hooked up. This is a bogus reading, which I confirmed by getting about the same reading with the engine off and no charger hooked up. Apparently some meters don't like trying to measure AC voltage across a DC source like a car battery.