Battery check

[Rodallg]

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?

[Gjac]

Rodallg wrote:
Any comments?

What are you using to charge the battery? Is it a small float charger? Manual car charger 6+ amps? Or a 3 stage smart charger? How long are you charging it for? How do you know when it is fully charged? You should let it sit overnight before taking voltage readings. By waiting several hrs like you stated you are just reading a surface charge. If you disconnect your neg cable or install a disconnect on the neg cable you should be able to last several months without recharging on a fully charged battery. I have an older MH also with a 7 year old Walmart battery and have a .4 amp draw without disconnecting the battery. A 2.5 year old battery should still be good unless it was severely undercharged for that period. I would get the 40 amp B&D or Stanley smart car charger if you don't have one already and fully charge it, then run the equalize function. Hope this helps.

[pianotuna]

Hi,

How long did you charge it?

[Rodallg]

Any comments?

[Rodallg]

After some time away from my issue I have decided to revisit it.
I removed the battery and brought it home to charge it. I removed it from the charger and let it set for a few hours, checked the voltage and it was at 12.8 and after checking every day for a week it fell down to 12.5. Would this be normal?
After I installed it I did an amp check and for the load to be 185 mA, pulled the fusses for the co2 and gas detector and I now am at 20 mA.
Are these readings ok?

[jerseyjim]

My motorhome is going for 12 years. My OPINION is not matter what battery brand you buy, 3-4 years is about it.
So, I buy mine at, say, SAMS' Club or WallyWorld...I find them (12 and 6V) a bit cheaper and last the same as "name" brands like Interstate.

FWIW.

[Dutch_12078]

Engine battery disconnects in RV's typically do NOT do a 100% load disconnect. Low draw items like ECM memory, radio memory, dash clock, etc, are normally wired direct to the battery, bypassing the disconnect.

[Kaz]

Rodallg wrote:
Yes I meant "12" and not "2", I took it to walmart and had them test it. They said it was good, they charged it to 12.58 vdc and the CCA of 775 out of 850. I can't believe it is good though. I installed it back into the MH for and checked the draw again and was still at less than .9 milli amp, so in the next week I expect it to be low again.

Let's see what happens. If the battery has about a 100-AH rating (Group 27 battery), it should still be at 85% or so after running your parasitic load for a week. Even a Group 24 battery (75 AH rating) should still be at 75% (12.4 volts). (Again, I'm doing this from memory ... which ain't what it used to be. Google the topic to make sure the voltage-charge numbers are right.)

Also, I just went back and re-read the thread. Are you saying that the measured current is with the chassis disconnect switch off? If so, 90mA seems high. That doesn't answer the battery question, but it's something to think about once you get that issue addressed.

The good news is that electricity is 100% logical, so if you're methodical, you'll find it.

Keep us posted,
Skip

[Rodallg]

Kaz wrote:

Rodallg wrote:
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.

You're saying "2.6" and "2.4," but I assume you mean 12.6 and 12.4? If that's right, then no, something is wrong. I don't have my tables with me, but I think 12.4 volts is about 25% discharged, which shouldn't happen overnight. Sounds to me like the battery is defective.

Skip

Yes I meant "12" and not "2", I took it to walmart and had them test it. They said it was good, they charged it to 12.58 vdc and the CCA of 775 out of 850. I can't believe it is good though. I installed it back into the MH for and checked the draw again and was still at less than .9 milli amp, so in the next week I expect it to be low again.

[Kaz]

Rodallg wrote:
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.

You're saying "2.6" and "2.4," but I assume you mean 12.6 and 12.4? If that's right, then no, something is wrong. I don't have my tables with me, but I think 12.4 volts is about 25% discharged, which shouldn't happen overnight. Sounds to me like the battery is defective.

Skip

[Rodallg]

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.

[Kaz]

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

[Rodallg]

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.

[pianotuna]

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.

[dons2346]

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?