Battery check

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

dons2346 wrote:
Even with a battery disconnect, there are still phantom loads present. CO detector, LP, the disconnect relay, etc. The only way to truly disconnect a battery is to lift a lead from the battery. I had the neg. lead disconnected and it dropped the amount in my original post.

Even then a battery can self discharge 2% a month.

How could you check amp draw if it is disconnected?

It was in series from the negative cable to the battery.

Hi,

Chassis = engine battery = with a modern vehicle *lots* of small loads.

I added a trik-l-start to mine, so my solar system now maintains the chassis battery in addition to the house banks.

Even with a battery disconnect, there are still phantom loads present. CO detector, LP, the disconnect relay, etc. The only way to truly disconnect a battery is to lift a lead from the battery.

Even then a battery can self discharge 2% a month.

How could you check amp draw if it is disconnected?

A)What do you have running? Its the chassis battery, the only thing on that I know of is the light for the chassis disconnect.
B)When was the last time you checked the water? I checked the water after taking it out, water is full.
C)Do this for a real check. Leave all the lights on, then when the batteries are dead.

Check the water in both, top off to the marker with distilled new water. Then remove the cables on one, recharge it at 2 amps.
(this may take 24 hours)per battery

I need to replace the chassis disconnect relay since I don't believe it is disconnecting. I'm doing the battery checks since it is dropping off after a week or so. I believe that even if the relay wasn't disconnecting it would draw the battery down as fast as it is. I'm suspecting the battery.

A)What do you have running?
B)When was the last time you checked the water?
C)Do this for a real check. Leave all the lights on, then when the batteries are dead.

Check the water in both, top off to the marker with distilled new water. Then remove the cables on one, recharge it at 2 amps.
(this may take 24 hours)per battery

While charging leave your charger above the batteries as gasses go down during charging.
Let it sit and do the other the same way. Wear gloves and safety glasses and use the normal safe procedures for this.

Reason for this is to RE-establish the charge in the batteries.
Make sure you wire brush all fittings and clean the cable connections .
You should be good to go.

Good luck