1 of 2 batteries is very hot!

[rickybobby]

2004 Classic. Two batteries both purchased same time last year. Batteries have been used consistently throughout the last year. AS has been hooked to 110 for last month without a single issue...until now. Smelt and then found battery on door side, furthest from converter to be very hot. Pulled it and had it tested. Batter is good but had 827 CCA when it was only rated for 750.

Could this be a bad converter that has allowed one of two batteries to overcharge?

Has anyone experienced this before?

Any ideas would be greatly appreciated?

Thanks!

[uncle_bob]

Hi

Battery capacity goes *up* when you get them hot. CCA is not a very good test for an RV battery (you care about amp hours). CCA is what you need to start an engine on a car or truck.

Keeping a pair of batteries "happy" when charging them in parallel is always a bit of a gamble. That's why you see people to to two 6V in series. Test both batteries and see what you get. If they are now mismatched, one will never do you much good.

Best guess (and it's only a guess) - the battery has an issue and the test didn't catch the problem.

Bob

[alano]

It's possible that your converter isn't working but not very likely. Measure the output voltage and see if it's a steady 13.7 V or so.

You probably have a single-stage converter, which is not recommended for extended charging periods. Your charger provides a steady 13.7 V or so and provides no temperature compensation. Better converters provide temperature compensation with a negative temperature coefficient - meaning that as the temperature increases, the output voltage decreases to better protect your battery. You likely overcharged your battery and the battery that got hot is probably unrecoverable and should be replaced.

Lots of folks replace their converters with three/four stage converters, but you can quite easily get along fine with the converter you have as long as you don't leave it connected to the battery for extended periods.

[SSquared]

How were the main wires connected to the batteries? You should have the main ground wire going to one battery, and the main positive wire going to the other. If both main wires go the the same battery, then the batteries will always experience unequal charging and discharging.

[jcanavera]

For what it's worth here is the charging recommendations from the manufacturer of your model battery.

Recommended charging information:

Alternator:
13.65 to 15.0 volts, no amperage limit.
Battery Charger:
13.8 to 15.0 volts, 10 amps maximum, approximately for six to twelve hours.
Cyclic Applications:
14.7 volts, no current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below one amp, finish with two-amp constant current for one hour for D34M and three-amp constant current for one hour for D27M and D31M.
Rapid Recharge:
Maximum voltage 15.6 volts (regulated), no current limit as long as battery temperature remains below 125°F (51.7°C). Charge until current drops below one amp.
Float Charge:
13.2 to 13.8 volts, one amp maximum current, time indefinite (at lower voltage).
Strictly adhere to all limits.

Obviously unless you have a smart charger, a 30 day connection without any voltage draw exceeds the limits for your batteries. It's probably time to consider battery replacement. I really wouldn't recommend an AGM for your trailer unless you upgrade the charger in your Classic. I've boiled out the electrolyte in my lead acid batteries on my 2004 Classic by leaving it plugged in as it sat in my driveway for a few weeks.

Sorry to see this happen. Those aren't cheap batteries. If you don't boondock a lot and don't want to upgrade the charger, you might consider going with the standard led acid Deep Cycle batteries which are around 1/3 the cost of the ones you have today.

Properly maintained the AGM batteries you have can give you about 3X the life of a typical lead acid deep cycle and can withstand a deep drawdown better according to the manufacturer's advertising.

Jack

[uncle_bob]

Hi

..... ummm .... errrr ..... "float charge 13.2 to 13.8V ... time indefinite ..."

That's pretty much exactly what the stock charger does when just sitting there. Current into the battery will be zero once it's charged. Since the two batteries are in parallel, they see the same voltage. You can't kill one battery with a "bad voltage" and not kill the other. They both see the same thing.

Bob

[DKB_SATX]

In the OP's shoes I'd have BOTH batteries tested. There could be a problem with the battery that's not getting hot that's causing the not-yet-dead battery to take the brunt of the charging. Did you have both tested, or just the hot one?

[Al and Missy]

Batteries age differently. The battery with the lowest internal resistance will take more charge current, but at a proper float voltage, that should not cause a problem.

Charge them up and then disconnect them from the trailer and each other. Measure the voltages periodically. I'm betting that the one that is getting hot has higher internal leakage and will discharge faster. If one is bad you should change them both. Get new batteries from the same manufacturer with the same date code.

A single stage charger is a compromise. If the voltage is high enough for a reasonably fast bulk charge, it will be too high for float. If it is low enough for a good float, it will take very long to bulk charge (the first 80% of charge).

Al

[Al and Missy]

Originally Posted by uncle_bob

Hi

..... ummm .... errrr ..... "float charge 13.2 to 13.8V ... time indefinite ..."

That's pretty much exactly what the stock charger does when just sitting there. Current into the battery will be zero once it's charged. Since the two batteries are in parallel, they see the same voltage. You can't kill one battery with a "bad voltage" and not kill the other. They both see the same thing.

Bob

You left out the part about "1 amp current limit". The stock converter doesn't limit current. It can't because it hss to power the 12V loads.

Al

[alano]

Al's right. There's no current limiting in the single-stage converter. The float voltage is typically 13.7 V but at 25 deg C. When the ambient temperature increases, if there's no temperature compensation you'll be stressing the battery. It's true that the so called "good" battery may have been damaged too, so it would be prudent to get that one checked out too.

[rickybobby]

Thanks to everyone for the inputs. I'm pulling them both...I will let you know what I find out.

[m.hony]

Lots of people have suggested that when you upgrade to AGM batteries you should also upgrade the converter/charger to a "smart" "3 or 4-stage" converter/charger such as Progressive Dynamics.
They may be right.
I have AGM batteries, but haven't upgraded my converter/charger.
Maybe I will get a round tuit one day.

[rickybobby]

Update...both batteries tested bad at one store. That store did not carry optima batteries so I went to a store that specializes in batteries and they retested. The batteries then tested good.

With that I cleaned all their terminals and made sure all connections were correct and hooked them back up and plugged into 110. HOWEVER, I switched the position of the batteries. It only took about 4 hours and the original battery that was hot, got hot again! So I think that is truly a bad battery...thoughts?

At this point I think I will be buying batteries after all. If anyone has any future ideas I would still like to hear them.

[m.hony]

The Optima batteries are $40-$50 less from Amazon.

[alano]

Personally I would replace the bad one with a new one from the same manufacturer and see how it goes. Batteries in parallel don't need to have exactly the same capacity. If the "good" one seems to work but doesn't have as much capacity as a brand new one, who cares. If the sum of the capacities of both batteries meets your needs then Bob's your Uncle.

Don't leave your single-stage converter connected for extended periods.

[Moflash]

Optima batteries are great as long as they are maintained with a 10 amp charger any more and they are toast prematurely....

[uncle_bob]

Originally Posted by Al and Missy

You left out the part about "1 amp current limit". The stock converter doesn't limit current. It can't because it hss to power the 12V loads.

Al

Hi

Which is a limitation of any converter that does not do full battery isolation. The typically touted 2,3,4 stage converters have exactly the same problem. Once you get to float, there isn't going to be any current into the batteries.

Bob

[jcanavera]

Not surprised that both tested bad. The fact remains that with a single stage charger you stayed connected for 30 days. As noted by the manufacturer of those batteries, 6-12 hours is what it takes to reach full charge. I think you really need to look at how you use your trailer and then determine what kind of replacement battery makes the most sense.

For me we always camp at sites with electrical power and we also carry a propane powered generator for power backup. Our only real use of the battery might be for operation of the hitch jack on departure and arrival and the maintaining of the fridge electronics when we are traveling and are running on gas. In that mode spending $600-$700 dollars on a pair of AGM batteries really isn't cost affective and lead acid with a cost of $100 each is perfectly acceptable.

Now if you rely a lot upon batteries, then AGM may be a great solution, the key then is treating those batteries to proper charging methods. If you can't manually adhere to minimizing the charge times, then it would make good monetary sense to change your charging system in your Airstream to a multi-stage charger.

I'm sure there are lot of folks here on the forum who can give you good recommendations of multi-stage chargers that will work with your Classic.

Jack

[m.hony]

...or upgrade to a Progressive Dynamics "smart" 3- or 4-stage converter/charger...

[Jammer]

Originally Posted by rickybobby

Update...both batteries tested bad at one store. That store did not carry optima batteries so I went to a store that specializes in batteries and they retested. The batteries then tested good.

With that I cleaned all their terminals and made sure all connections were correct and hooked them back up and plugged into 110. HOWEVER, I switched the position of the batteries. It only took about 4 hours and the original battery that was hot, got hot again! So I think that is truly a bad battery...thoughts?

At this point I think I will be buying batteries after all. If anyone has any future ideas I would still like to hear them.

You have a shorted cell on the bad battery. It's not unusual.

Just replace the bad one and leave the other one in service. Despite the conventional wisdom to the contrary, it will work fine.