I think the 12v agm battery is starting to go on our 03 prius. It wouldn't start after 4 days no use but did after 2. What is a healthy resting voltage (with nothing turned on) for this agm battery as I'll check it with a multimeter? What is considered an unhealthy voltage? Thanks, Graham
If the battery is anywhere near 10 years old, don't bother......just get a new one. If you are stealthy enough to catch it when there really IS absolutely no load in it, it should be around 12.8, minimum. Less than 12.4 indicates the battery is going bad or it isn't being charged. About the only way to get a good test is taking it out of the car, putting it on a small charger (~2 amps) for about 8 hours, letting it sit for one hour and then checking the voltage AND doing a load test. But then see sentence #1 above.
