Battery Weirdness

[Dennis M]

Batteries in the Volvo are a little over two years old. Truck has been parked here in the RV park since mid-December. Saturday I started it to pump up a yoga ball - yeah, I have a smaller compressor, just not with me!

 

Anyway, when I turned the key on, the dash read-out showed 12.2 volts. Hmm, that's a little low. Started up fine and ran for about fifteen minutes. Yesterday I went to get some things out of the sleeper and realized that the flourescent overhead light in the sleeper was on. Apparently had been on for some time. Batts so low it no longer lit.

 

OK, borrowed a fairly sophisticated battery charger from my neighbor. It showed 7.7 volts (!) when I attached it. Put it on 30 amp fast charge for a couple of hours. It showed 100% charge, but said it was reading a 6 volt battery! When I turned it off it showed 7.1 volts. Put it onto 5 amp charge, it now shows it is charging a 12 volt batt at 29%. Talking about four batteries with base bars here.

 

Last evening it was showing 43%, this morning 100%. But when I turned it off it only was reading 12.2 volts. Put it onto 3 amp charge and it shows 59% and charging!

 

Now I'm pretty good at 12 volt systems, made my living as a mechanic for a number of years and was ASE Master many moons ago, but this one has me puzzled. Any ideas?

[rickeieio]

I am not a mechanic. Rarely sleep at Holiday Inn. But I would remove one buss bar and check individual batteries. Sounds like a bit of corrosion, and/or a loose terminal.

 

I've had a rash of loose terminals lately. Like, a dozen or more. It gets old.

[Broncohauler]

When you hook up the charger,make sure you put the positive on one end of the battery bank and the negative at the farthest end of the battery bank away from that positive.

 

Also check your voltage the same way. If you still have a problem I would isolate each battery from each other and check the voltage independently.

I had a problem with mine in after using a hydrometer found out I had one cell out of three batteries that was bad and ended up replacing all three batteries.

[OldFlySwatter]

While you've got the buss bars off to clean them, try fully charging each battery sepreatly to where it's showing at least 13.6 volts. Let it sit for 24 hours and then check each batteries voltage. This should show you if one or more of your batteries has developed a bad cell and is draining the other batteries. Two plus year old batteries can and do go bad. Hope you find your problem.

[lenp]

Perhaps the smart charger you used thought the 7.7 volts meant it was a 6 volt battery and charged it accordingly - essentially discharging them even more???

 

Lenp

[Dennis M]

Perhaps the smart charger you used thought the 7.7 volts meant it was a 6 volt battery and charged it accordingly - essentially discharging them even more???

 

Lenp

Think you are right on that one Len. When I dropped the charge rate to 5 amps it started reading them as 12 volts.

 

I have pulled the buss bars and started charging them one at a time. The first one came up to 13.3 volts on 5 amps. Have it running overnight on 3 amps.

[lenp]

With a charge rate of three amps it is going to take a LONG time to reach full charge. I would expect these to be pretty good sized batteries that will probably need 50-60 amp hours each (or more) to reach full charge. A three amps that could be 20-30 hours each.

 

Recommend you charge each of them an equal length of time to get them as close to the same charge as possible. Specific gravity readings would help to determine if they are all equal. Putting a somewhat discharged one in parallel with a fully charged one will result in the discharged one drawing the other(s) down.

 

Lenp

[Dennis M]

Update: So far three good ones, coming up to full charge individually with no problem. Taking 4-5 hours on 5 amps to get to 95% and then I'm letting them run at 3 amps overnight to finish off.

 

Sick as a dog the last two days so I haven't pursued anything else. Beginning to wonder if I have a positive cable shorted to ground somewhere. That will be the next check if the 4th battery comes up healthy. Fortunately I have plenty of time to investigate since we don't plan on moving until May or June!

 

Can't check specific gravity since they are sealed batteries.

[Jack Mayer]

You are taking the right approach, now. Once you charge up each battery individually it is time to load test them individually. You may get "a charge" but still have a bad or weak battery. If you do have a bad battery that will not show up on the charger in most cases unless it is a very smart charger that can load test. So you need to load test them to definitively determine if one is bad. If you do have a bad one I'd replace them all unless the batteries are pretty new....it is a judgement call on that. But if they are over two years old, then all should go at once. IMO.

 

If the batteries recharge OK and check out OK on the load test then most likely you have a loose or dirty connection. Make sure you check and clean any shutoff switch you have....many people forget them. Check your amperage at the starter during a cranking attempt and that will tell the story....assuming you have a clamp meter that will handle the amps.

[Dennis M]

Update: disconnected the batts and charged each one individually. All four came up to just above 13 volts and stayed there. Let them sit for a couple of days, hooked back up and all seems fine. Started right up, showing 14 volts while running, which is normal, and settled at 13.6 after I shutdown.

 

Must be I just really flattened those suckers without realizing it. I'm sure it did the batteries no good, but we will see.

 

Thanks for all the advice guys.