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I've been dealing with an electric issue that has me checking the voltage on my battery. My INDY "Master Mercedes Mechanic" told me readings as low as 12V are "normal" even for a new battery in a vehicle that is not running.
According to the stuff I read online, the battery should be 12.6V to 12.8V when not running.
I'm asking the people here what they think a healthy battery should read when not running after sitting 12 hours?
Please chime in with your comment. No right or wrong answer. I'm trying to get an idea what real-life owners have experienced.
C230 Sport Coup + 2006 W164 ML350 + 99 Ford Escort RIP
Well it's a 12v battery so I've never had any expectation of it being any higher. A little lower, a little higher is OK.
The measure of it's health is the CCA is Cold Cranking Amps.
Depending on what battery came with the car that could be anywhere from 600-900 when the battery is new, and
decreases over time until it no longer turns over the car or won't charge.
Open circuit (that is, with the battery out of the vehicle or with one of its terminals disconnected) 12.6 volts is normal for a healthy charged battery. When you put the vehicle in accessory mode (one start button press / engine not running), the electrical load can be typically 10A which can draw the battery voltage down to 12.0 volts in only a few seconds. Cranking the engine can pull the voltage down momentarily to 10 volts, whereupon engine running, the alternator kicks in and the battery terminal voltage increases to as much as 14.8 volts indicating charging. But many factors including the age/health of the battery, its charge state and environmental temperature affect the battery voltage under various load and charging conditions. If you're troubleshooting electrical problems, start with a good battery and connect a 10 amp charger to it while taking measurements. When you begin removing components and making repairs, disconnect the battery's negative terminal and secure it away from the battery.
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