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TJHUB · 05-29-2020, 09:38 PM

Last Fall, I purchased a battery tender to maintain my chassis and house batteries. I'm not exactly sure how, but both 6v house batteries ran dry of water over the Winter. I installed them in the coach, and they were at 6.4v and wouldn't power anything. I checked the water levels, but there was none. None to the point of each battery took about a gallon of water to fill.

I just returned from a 5 day trip, and within 3 hours or so, the house batteries were down to 10.2v with nothing running, but the disconnect was on. My guess is that I killed the batteries which is very upsetting to me. Live and learn I guess...

So this brings me to my question. Could I just replace the (2) 6v batteries with a single 12v ? Why? Because I've owned this coach for nearly 3 years, and the ONLY time I ever run off the house batteries is to run the fridge off LP the night before a trip and turn the lights on for a few moments when needed. Once the coach is running, the engine charges the house batteries within minute or so, and I've never needed the inverter for anything. I just don't see why I would need more amp hours than a single 12v deep cycle could provide. I only use the coach at full hookup campsites, and don't see that changing any time soon. So for me and my uses, won't a single 12v deep cycle battery do just fine?

Jim_HiTek · 05-29-2020, 09:53 PM

No, don't replace your 2 6 volt with one 12 volt. Your 6 volt deep cycle are design for the various draws and phantom loads an RV will put on them. So, look at Costco for a couple new 6 volt deep cycle.

Then in future, whenever you leave the RV for more than 3 days, just disconnect the ground lead from the 12 volt chassis batteries and the jumper between the 6 volt house batteries. They'll lose a little over time but I've left mine like that over 3 winters in Fairbanks and they needed a bit of charging in the spring but they survived. Healthy batteries can withstand -70 C so no worry about that.

If you do that, you can expect 12 years out of the batteries.

Now, your converter...it's over charging. Find out why. It's probably bad.

twinboat · 05-30-2020, 03:56 AM

You'll be fine sticking a GP 27 or GP 31 maintance free battery in place of the 2, 6 volt batteries.

I got my GP 31 at Sams Club . Maintance free, ( no caps to check ), deep cycle, for around $100 .

Seems like your battery maintainer may be over charging your batteries. Best to disconnect them and let them sit.

Winemaker2 · 05-30-2020, 05:14 AM

Quote:

Originally Posted by twinboat

You'll be fine sticking a GP 27 or GP 31 maintance free battery in place of the 2, 6 volt batteries.

I got my GP 31 at Sams Club . Maintance free, ( no caps to check ), deep cycle, for around $100 .

Seems like your battery maintainer may be over charging your batteries. Best to disconnect them and let them sit.

I agree and have confirmation from East Penn (mfg of Sam's Club Duracell battys) that their AGM GP31 has the same deep cycle performance as the 6 V GC2s.
AGMs will avoid the water issue and have lower self discharge.
You do need to check for over charging.
Make sure the maintainer is a multi stage and not a constant fixed Amp charge. I have had excellent results w Battery Minder maintainers.

TJHUB · 05-30-2020, 05:58 AM

Thanks so much for the responses. I did expect to see that I need to stick with (2) 6v batteries, and I still might. However, a single 12v seems to fit my needs and will have all the performance I may ever need. I will look into the batteries suggested.

I used a Deltran Battery Tender with (2) 12v outputs. I used one on my chassis battery, and the other on (2) 6v house batteries in series. The chassis battery is fine.

I don't recall checking the water levels in the house batteries, so maybe they were low when I connected them to the tender, and over the Winter months the low water levels caused the tender to overcharge them burning the water off? I am so disappointed I let this happen.

Persistent · 05-30-2020, 06:50 AM

You can probably continue to use the damaged batteries because you don't need much capacity. You also may be able to restore some additional capacity by "conditioning" the batteries.

A 15 or 16 volt charge for a period of time may convert some of the sulfate crystals that have formed on the battery plates. Some high end RV chargers have that function available. Otherwise a service shop or battery store may be able to do it.

On the new battery question. You never need more battery than you use. What is left in your damaged batteries may be enough. You may wish to get an AGM battery. When stored fully charged, they will last for about 12 months without any kind of tender or charger. Flooded cell batteries in good condition are good for about 6 months.

Your previously new batteries were probably over charged by the battery tender. Dump the tender.

On the other hand, not checking water levels in a flooded cell battery bank periodically while being charged is a major error. Lead/acid batteries consume water while charging. That is how their chemistry works. High ambient temperatures compounds the water loss issue.

Generally, the best battery tender is the inverter/charger/converter installed in your RV. If you remove the batteries from the RV for storage, make sure they are fully charged to start. Unless the batteries are old or in bad shape, they do not need charging for 6 months or so.

I wish you good luck and happy trails ahead!

Mark_K5LXP · 05-30-2020, 11:47 AM

It's surprising that a battery tender would do that, since that's their primary purpose. I've been using one flavor or another of those for years to hold up all manner of starting and storage batteries for extended periods without an issue. Not to say one can't go south but something sure did. If you wanted to go through the throes of attempting a recovery you've got nothing to lose but just from what you're saying it doesn't sound promising.

I'd be on board with the idea of trying a 12V battery even as just an experiment. Maybe it would give up quicker than two GC-2's but it's a lot less expensive too. In light service most any battery is good for at least 4-5 years so even if you replaced it at that interval I think you'd be money and convenience ahead of GC-2's. One way to find out...

Mark B.
Albuquerque, NM

TJHUB · 06-14-2020, 05:48 PM

I tried to recondition the GC batteries, but they will only hold 12+ volts for 30 to 60 minutes. They will hold 10.0 to 10.4 volts for many days. They will drive my slides in and out, as well as keep the disconnect running to operate everything. This had me thinking good enough for this season, then get a replacement next year. But...

During my last 4 day trip plugged in at a campground, I noticed the steps above the battery compartment were rather warm. Would this be because the batteries are constantly being charged because they can't get to a full charge? Isn't this a bad thing for both the batteries and my on board charger?

I guess I'm wondering if I should just bite the bullet and buy a battery?

Jim_HiTek · 06-14-2020, 07:18 PM

Yeah, batteries heating up when they are ruined isn't a good thing. A 100% discharged battery is 10.5 volts, and you're seeing less than that. I assume you serviced them so they have plenty of water...but it they are warm, that still points to a bad converter or a bad battery.

How 'bout measuring the voltage across the batteries while plugged into shore power? Wait a few minutes after plugging in. That will tell us something.

A bad battery with shorted cells will overheat and it's not good when it does. And the fact that yours fall to 0% charged after a few minutes says that yeah, they are bad now so you need to replace. But do check the converter TOO.

Good luck. Note that I've limped along with not-very-good batteries for years when I needed to. But they weren't overheating either.

Mark_K5LXP · 06-15-2020, 07:06 AM

Quote:

Originally Posted by TJHUB

They will hold 10.0 to 10.4 volts for many days.

Sounds like a bad cell. If they're flooded batteries you can check the electrolyte in each cell and usually find the culprit. Another way to tell is put a moderate amount of charge current into them (~20A) and the good cells will gas, the dead cell will be still. If you leave it sitting long enough that way the good cells will start to get warm but the bad one will be cold.

There's no recovering from that, to limp them along in that state will mean perpetually low voltage, heavy gassing during charging, high water use and elevated temperature as you reported. Technically it's "bad for the batteries" but they're already toast. It shouldn't hurt your converter, other than maybe diminishing available 12V power to other circuits as it heats up your batteries. They won't last long this way, this kind of cycling will considerably shorten the life of the remaining good cells.

Mark B.
Albuquerque, NM