Battery check

Kaz wrote:

Rodallg wrote:
Checked my chassis battery 1 week ago and it was at 12.17 vdc (with the neg. lead disconnected), today I checked and it was at 11.88. Is this an expected drop? Battery is 2.5 years old. I checked the amp draw and it measured 0.10 on the 10amp scale. I brought it home and put it on a charger and try measuring it again. Last resort was to take it somewhere and have it tested.
Any thoughts?

It's kind of an art form to measuring state of charge with a voltmeter (dissipating surface charge and all that), but I agree: Something's up. A fully charged battery (after a rest period) should be around 12.65 volts, so you were only about 50% charged when you started. Maybe the battery was not recently charged, or it's not holding a full charge.

But even still, it shouldn't drop that much in a week. 11.88 volts is essentially 100% discharged. 100 mA is slightly high for a parasitic load, but not that high. Of course, measuring on the 10 amp scale is pretty rough for the mA range -- you probably want to get a reading on the mA scale, but still... something's not right.

I guess I'd do two things. First, disconnect all loads, fully charge the battery, let it sit for 24 hours, put a small load on it for 5 or 10 minutes, wait for a few minutes, and then check the voltage. It should be 12.65 or thereabouts. And, if you can, use a hygrometer to check the specific gravity of each cell. Each should be about 1.265.

Assuming that checks out, leave the battery disconnected and check it again in a week. It shouldn't change.

Then, assuming you've got a good battery, I guess the problem is the parasitic drain. Technically, anything less than 100mA is OK, but really it should be down in the 35-50 mA range (or less). What I've done for other folks looking for similar problems is to suggest putting a meter on the battery (like you've done), and then pull fuses one-by-one looking for the one that eliminates the drain. You might find something like a TV antenna amp switch left on.

If none of that works, then ... hmmm ... don't know. Let us know and we'll figure out the next step.

Good luck,
Skip

Thank you for the help.

I brought the battery home and put it on the charger, disconnected at full charge (I believe it was in the 2.6 range), checked it 24 hours later and it is now measuring 2.40. is the .2+ drop an acceptable drop? The battery is from Walmart, I guess I could have them check it but I don't want another Walmart battery.