Engine stays running without key in ignition (and more!)

It's actually a mystery to more people than you'ld imagine. Took Nacho over in the moparts forum to explain how the system worked before I finally got on track.

Righty Tighty said

In fact, when my charger indicated the battery was fully charged/maintaining, I checked the battery with the voltmeter and it showed 16.6 volts. Could the charger have overcharged the battery? It's not exactly a high quality unit, just something I picked up from WallyWorld a few years back.

Click to expand...

I agree that doesn't seem right. Do you have some other batteries you can check the voltmeter with? Something like 9V or 3 or 4 C cells could work too if you can keep them lined up or in a holder.

@toolmanmike might have some insight both the charger and the meter, if you want to post the specific models.

My understanding of wet cells is the most they can charge up to is around 12.8 Volts. I can't imagine how there could be higher than that unless its a 16 Volt battery. Immediately after charging there a slightly higher voltage due to something called surface charge. So often it will measure 13ish volts right after shutting the car ogff. If you flip the lights on for a couple seconds, the surface charge disappears. There's really minimal stored energy in the surface charge, and it will go away pretty quickly even without turning something on.