New Battery boiling

[mxdad290]

I purchased all new batteries for my coach and chassis. I hooked them up and went to test the slide. The slide worked as it should but my son was standing by the battery compartment, which is still open and said the chassis battery seemed like it was boiling. It was and seemed to be getting worse by the second. I quickly unhooked the ground and it stopped. What caused this? I am 99.9 percent positive it is hooked up correctly.

[twodownzero]

My new batteries bubbled for an hour or so when first installed. They were mostly charged but the solar charged them the rest of the way and they bubbled. Haven't noticed it since then though.

[wa8yxm]

Two common problems
Connecting a pair of 12 volt batteries in Series (That's a no no)
Connecting a pair of 6 Volt GC-2 in parallel... (LIkewise)

How to connect
-12+
-12+

Or

-6V+-6v+

Either method gets you 12 volts from the left to the far right end of the connection.

[dougrainer]

You MUST get a Voltage reading at the Chassis Batteries when they are boiling. You seem to have a 1999 Thor product. Even if you have a BI DIRECTIONAL charge system, That will NOT cause the Chassis Batteries to boil. If so, then the Coach would boil. Also, The fact that the chassis are boiling almost immediately when you hooked them up points to a connection problem. Rarely will batteries boil that quick, UNLESS, they are defective batteries to begin with. Now, IF you have an Inverter/Charger which will have a HIGH BULK rate charge when first connected to 120 voltage, AND you somehow hooked the Inverter/Charger POS cable TO THE CHASSIS BATTERIES, that may cause them to boil. Chassis batteries are NOT meant to have a high bulk charge and will overheat and boil from a bulk charge. A simple test would be to disconnect the Chassis batteries and then check if your Inverter is powered if you have an Inverter. IF it is NOT powered, then you connected the Inverter to your chassis batteries.
AS the other poster stated, when you replace batteries and then you get a failure. 99 percent of the time it is you failed to connect correctly. I speak from 40 years experience. I have had customers swear they did not connect wrong and when they bring the unit in, I find the problem in less than 5 minutes, They did connect wrong or missed a cable or 2. Doug

[schlep1967]

MrWizard wrote:
old did not boil

new is boiling

something is connected wrong

Unless old did boil and that was why it needed replaced.

Verify that the cable you had hooked to negative post goes to the frame or a good ground nearby. If it does you need to have your charging system checked out.

[MrWizard]

old did not boil

new is boiling

something is connected wrong

[DFord]

Did you measure the charging voltage being sent to the battery with a voltmeter/multimeter? Could it be the new battery was calling for a boost to top it off that would taper off when it reached full charge. The converter-charger on older RV often boiled the water out of batteries because of its fixed charging rate. The newer ones should end up with a "float charge" being applied.

[mxdad290]

I did have the motor home hooked up to regular outlet at my home for lights in the rv. But did not have it cranked.

[mxdad290]

Unfourtnaley no I did not take a picture. I did of the two deep cycle, but not of the cranking battery. But I don't think I got it wrong. Since there were only two to one post and they are connected together and one to the other post. I'll get a picture tomorrow.

[oldave]

Did you take a picture of the cables ?

Replacing batteries seems so simple but it seems like when someone doesn't
take a picture and draw a diagram too they inevitably get mixed up .

Before changing the cables take a picture and post it here .
The folk here are so helpful and they will help you figure it out .

I would not hook the batteries back up until you resolve the issue .
You may have a defective charger that is charging full blast .
At any rate a boiling battery is dangerous .

[wolfe10]

Tell us what batteries you have and how they are hooked up.

Sure sounds like a mis-wiring! Perhaps something like charging a 6 VDC as if it was a 12 VDC.

[opnspaces]

were you plugged into shore power?

I would verify the battery hookup. On trailers it's usually black is positive and white is negative. I'm not sure if that holds true for motorhomes.

Do you have a meter that you can use to do a continuity check between the wires you were using on the negative post and a good ground point? you should have almost no resistance with that measurement. If you are reading high resistance or even OL you are checking a positive wire. make sure you are checking the wire to ground, DO NOT put either probe on a battery terminal or you'll blow a fuse or fry the meter.