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Is a battery that tests good but has a low max voltage still useable, or is it time to replace?

This car is mostly used in winter, so other times I use a battery maintainer once per week. If I disconnect the battery, charge it, wait 12 hours, and check the voltage, it is 12.45V on my Fluke meter, T = 76F.

So I brought the battery to AutoZone, and their battery tester showed the battery was Good, but needed a charge. I had AutoZone charge the battery, and the voltage results were the same 12 hours later.

It’s a maintenance free battery, so there are no ports to access the cells.

Good, Needs Charge
CCA: 730
State of Charge (Soc): 65%
Cranking Health: PASS
Reserve Capacity : OK

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  • In a lead-acid battery, the voltage gives you a measure of the % charge (i.e. it's 85% charged if voltage = XXX) But it doesn't tell you much else about the health of the battery. It's a "guideline" at best. It doesn't tell you the actual battery capacity either (i.e. how big is the gas tank). Just that the tank is some % full. The test the shop does is a load test, where they actually pass (for microseconds) a very high current and measure the voltage drop. Then they extrapolate to a "good/no good" conclusion. This is also more of a "guideline".....
    – Kyle B
    Commented Aug 16, 2022 at 18:12
  • A proper battery test would load the battery with high current for several seconds. But to do that you need a huge power-soak. Shops used to have big testers that needed to be rolled around (too big to carry). But they've mostly been replaced by those small digital hand-held things (probably with the result they sell more batteries than people really need). Bottom line ... When it's cold does the engine crank "vigorously"? If you turn on the headlights are they dim?? Those are great indicators of battery health.
    – Kyle B
    Commented Aug 16, 2022 at 18:14
  • @Kyle B -- Thanks. Will check the headlights next time. I have an Innova monitor meter in the cigarette lighter, but I'm not sure I trust it since the voltage it displays is definitely too high compared to my meter readings with 3 different meters.
    – 356V
    Commented Aug 16, 2022 at 18:56

1 Answer 1

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If this is a new battery, take it back to AutoZone and have them replace it. You should be able to charge it to either maximum or very near it.

If this is a battery you've had for a while, how old is it? Typical batteries last around five years. As the battery is used and goes through its recharging process, it can sulfate which is to mean, sulfur crystals will collect on the lead plates and limit the ability of the battery to charge up fully.

If the battery is somewhere in between new and five years old, you'll see a lessoning of how well the battery can be charged. A battery will still work just fine in most vehicles at 12.45vdc. As long as it is working and starting the vehicle, it shouldn't worry you too much. If you're getting close to that five year mark, you really should think about replacing it.

One word of caution. Batteries take a lot of beating in really warm or really cold conditions. If you see extreme temps in either direction, you might want to get a new battery if it's near end of life.

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  • Thanks. Battery age: 4.5 years old. Many years ago, I bought non maintenance free batteries, and those surely seemed to last longer than 5 years, and I did monitor the fluid levels. From other posts I've read, the AGM batteries are also supposed to last about 5 years, so I guess that would not help me.
    – 356V
    Commented Aug 16, 2022 at 18:01
  • @356V - If the battery is 4.5, I'd "think" about preparing to replace it. If the battery specifically says it's good for 7 years (or some such), then maybe not. However, if you're having problems getting it charged to the appropriate level (usually 13.1vdc is around the "max" charge level), I'd start looking. You know, as soon as you put this off you're going to have issues and it'll need replacing at the most inopportune time :o) Commented Aug 16, 2022 at 18:07

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