Boiled one of two 5th-wheel batteries

[Traveler1960]

Greetings all,
I am a new user with a problem.

I had newish batteries in my 2011 Montana (purchased batteries this year). I have the smart converter with boost mode.

Anyway, the rig was plugged into my home AC for 3 weeks and during this time I had no issues. Batteries were cool to the touch, the voltage was good, and the led converter was showing that it was in float mode. Then, about 12 hours before my departure I hooked up the truck so that I could leave early. So now the truck and 5th-wheel are plugged together with the stock 8 point cord, and I also left the AC plugged in to keep the frig cool. Next morning, one of the two batteries boiled dry or almost dry and it was so bad that the LP alarm was alarming too. Scary stuff, hydrogen enough to set off the gas alarm!!
So here is my thought, the truck connection made the converter see lower voltage that real at the 5th-wheel batteries and this caused the converter wizard to switch to boost mode. BWT, boost mode is 14.4 VDC@90 amps.

Does any of this sound as a reasonable explanation or does anyone have a better thought?

Thank you much!!

[Traveler1960]

Batteries have been replace and thus far, all is well. I was able to contact the converter manufacture too, and they sent me some testing instruction. Thinking back to the three weeks of charging I did before the morning of the event I recall seeing about 12.5volts at the post, and although this registered with me as normal, I know a fully charged battery will reflect 13 to 13.5, not 12.5. Best guess at this point is; I just had a bad cell or bad battery. Time and trial will tell. Battery replacement was free, as I had purchased them from Costco, and following my honest tell of sorrow and woe, they said that they had observed some returns on bad batteries this season. The didn't bat an eye about it and this made my day. I have also added a battery hydrometer to my collection of battery tools and I will now start checking each cell as part of my battery maintenance.
I thank everyone for the quality response to my meltdown (pun indented) and I will update this post should something change.

For now I will end this story with a two thumbs, a smile, and an oldie but goodie, live long and prosper.

Traveler1960

[Coach-man]

While you are at it, at least get the TV batteries checked! The only thing that changed in your scenario was you connected the TV so you could get a early start! You would then have the two batteries in the RV, plus the one(s) in the TV connected to the charger! Was it the batteries, was it the wiring??? Your GMC has a constant HOT connection to your 5th wheel batteries when plugged in, and that may have triggered the change that "fried" your batteries!

[Traveler1960]

Thanks everyone who responded. Read all the responses again and this is just to fill in some gaps you asked about.
I have two batteries in the fifth wheel, both bought at the same time, maybe 5 months ago. My care of the batteries is up to par, check them often. Only one battery was hurt. Agree about it not charging the truck (small wire there), but that was never a concern. The point I was making about the truck was; because of the small wire and it being far from the plug, it may not reflect the actual voltage of what the truck batteries really were, long small wire creates a voltage/current drop.

Tomorrow I will replace both batteries and do some more testing, but in all likely hood I will not do too much while on the road. Rather not cripple my trip. I have a master shutoff for the batteries and I am connected to power for now, so I will get along until I have a better place to work on it.

If I am able to determine the factual cause I will report back to all. You never know when someone else could benefit from my misery, lol.

Thank you again for all your kind responses.
Cheers

[Old-Biscuit]

During those 3 weeks rv was plugged in to house AC power and converter was charging/maintaining rv batteries.............did you check water levels????


Bad cell....bad battery

[Traveler1960]

Michelle.S wrote:
My GM the charge line to the RV is always Hot.
Are you sure the battery in the TV is up to snuff?
Because we're planning an early get-a-way in the AM, my TV is hooked up right now, same as I've done many times. If stopping for an overnite we try to stay connected and as long as the RV is plugged in I don't disconnect the cord to the TV. Been doing this for years and never a problem.

The battery was new this year, but I suppose It could have just failed. Do you have a converter with a high power boost? I know some don't.

[lc0338]

Since your truck is wired different... make sure your batteries are wired correctly. You did not mention if you have 2ea 12 volt or 2ea 6 volt batteries. If both batteries are same age and same maintenance and wired correctly you are better off getting 2ea new batteries because the other battery may be on it's last leg. Also not good to pair an old and new battery. It makes the new battery do all the work and usually lowers it's life.

[Michelle_S]

My GM the charge line to the RV is always Hot.
Are you sure the battery in the TV is up to snuff?
Because we're planning an early get-a-way in the AM, my TV is hooked up right now, same as I've done many times. If stopping for an overnite we try to stay connected and as long as the RV is plugged in I don't disconnect the cord to the TV. Been doing this for years and never a problem.

[lc0338]

Even if the plug is "hot" when the ignition key is in off position... The wiring to the vehicle plug is very small and can only carry a few amps. I really can't believe it would be enough to "fry" an rv battery. One of the things that can happen is with the vehicle plug hot when ignition is off set's yourself up for the rv to drain your vehicle battery.. and one of the reasons the plug is normally off with the ignition key. Without knowing how old your batteries were or how well you have maintained them it would be hard to say but I seriously doubt plugging your truck in had much to do with the failure.

[Traveler1960]

lc0338 wrote:
There could be something wired differently but I believe normally when the vehicle ignition is in off position there should not be any power to the vehicle plug. I suspect while plugged into AC the converter is doing all the work and the batteries are just maintained. I'm thinking kinda like timflood. How long ago did you add distilled water to the batteries? The still need to be checked and watered even when on shore power.

Good point about the power off with key off, but in my trucks case, normal or not, it is always hot. I will check if that is an option I can change. The water was topped off within the three weeks of being on the AC, and because it was on AC I made sure they remained full. Like I said, this is an odd one for sure. Fine for weeks and not a hint of problem until the truck was connected. I normally never do this except while prepping for an imidiate departure, but again, I wanted it ready as possible for the morning.

Very odd indeed. Never ever had anything like it happen before. I alway disconnect truck firm RV when I get to destination too. ALWAYS, and I need the truck as the get around the area vehicle.

Back to drawing board as they say.

[lc0338]

I suspect the lp gas alarm was going off not due to hydrogen gas but simply because it lacked proper battery voltage for power.

[lc0338]

There could be something wired differently but I believe normally when the vehicle ignition is in off position there should not be any power to the vehicle plug. I suspect while plugged into AC the converter is doing all the work and the batteries are just maintained. I'm thinking kinda like timflood. How long ago did you add distilled water to the batteries? The still need to be checked and watered even when on shore power.

[Traveler1960]

timflood wrote:
I think you just had a bad battery, east to test your TV. It sound just like you had a little bad luck with the batterys. I would still check out the electrical stuff.

Thank you for the prompt reply.
I wouldn't doubt that possibility, but I can't dismiss that for three weeks on AC, not a problem, then when the truck was connect it fried in 12 hrs. Just odd IMO.

Have to wait to buy new after the Labor Day holiday, then try to duplicate any issue with converter. Not to the same degree of course, but if the battery was not bad, then I have an issue.

[timflood]

I think you just had a bad battery, east to test your TV. It sound just like you had a little bad luck with the batterys. I would still check out the electrical stuff.