Best battery choice

[TipS]

I recently purchase an '05 Monaco Diplomat in great condition but for the house batteries. The RV dealer did install new chassis batteries but the house batteries are weak and won't hold a charge overnight. The previous owner (1) had the originals replaced at some point with 12 volt AGM batteries and hooked them up in parallel. My voltage drops overnight to around10.4 or so. The generator won't start at this level without starting the coach engine (400 hp Cummins) but once the engine is started the voltage comes up and the generator will start. My question is obvious...should I go back to the 6 volt series-parallel setup or simply replace the 12 volt AGM's with a new set of deep cycle batteries. I think these AGM's are Lifeline but I can't see a name label on them anywhere. Any input would be helpful.

[Bigd9]

IMHO, I suspect something else is wrong. A 7 or 8 year old coach already with the original batteries gone, and their replacement batteries also bad seems suspect. The AGM batteries should be very much alive and well. If it was me, I would start by checking the power draws the coach puts on the batteries. You indicated the battery voltage drops to 10.4 volts overnight. Another assumption is that is without being plugged in, right? What is pulling the batteries down? You can get the batteries checked at several auto parts stores. At least that way you would know if the batteries are good or not.

Again, if it was me, and I was looking for replacement batteries, I would go back to the Trojan 6 volt batteries.

[Bigd9]

Oh, I just noticed that you are new to the forum. Welcome Neighbor!

[ScoobyMike]

Life cycle of lead-acid batteries depends upon # & depth of discharge cycles, storage temp, % charge when stored & electrical current profile of charging system. Even under optimum conditions expect your batteries to be at end of life after 7 years. Run them dry and you will kill them. 6 V batteries have thicker plates & more liquid than 12 V. They don't require attention nearly as often as 12V.
If the dealer put in new batteries, they should be good (no matter how cheap they are) it does sound like you have a charging issue or a high current drain on the system.

[clyon51]

If the AGMs do test bad and it were me, no doubt I would replace with Trojan T105s or Interstate U2200s.

[wa8yxm]

Regarding the comment about "original batteries gone"

Many folks (just read the many threads here) have fallen for the myth that AGM are better, and I do admit there are conditions where that might be true, The result is these mislead folks will take out a perfectly good set of flooded wet cell batteries (Such as the ones the last respondant recommended) and put in a pair of inferior AGMs.

4 years is about right for AGM's. Though the often do last much longer,,, Many companies that use AGM's and treat them much kinder than we do, replace them every 4 years.

[Mr_D]

We replaced the OEM U-2200's at just short of 10 years. We were headed out on a trip to AZ and I didn't want trouble on the trip. They were still doing pretty good even at that age.
Nothing magical about AGM's as was said above. If you have limited room to service batteries then maybe you should use them, otherwise flooded wet cells are best.

[jwinston]

Is it possible that your refregarator is running the batterys down ie using AC thru inverter?

[Jon Mopar]

Check the fluid levels in the batteries. I have Interstate Workaholics. They weren't really holding a charge, then I found out the levels were down (these aren't a sealed battery mind you). I topped them up, now they're A1.

[wa8yxm]

Originally Posted by Jon Mopar

Check the fluid levels in the batteries. I have Interstate Workaholics. They weren't really holding a charge, then I found out the levels were down (these aren't a sealed battery mind you). I topped them up, now they're A1.

I hate to tell you this Jon but the O/P said he had AGM's in there

AGM's are SVRLABs (Sealed, Valve regulated, Lead Acid Batteries) and thus there is no way to check the fluid levels or to add fluid, This is one of the reasons they do not outlast well maintained U-2200's

Somewhere else I got flamed for saying AGM's do not last as long, The man pointed out Lifeline's claim of 1,000 charge'/discharge cycles.

Well, assumign you run them down to half, that's about six years. Max.

Run them down more (And folks claim you can do that with AGM's and the time is life is shorter

The same poster claims 300-350 for Flooded wet cells, that's 1-2 years

My U-2200's are 7 years and going strong in spite of a few times running them way below 50 percent.

My AGM's are dead and gone in 5. Replaced them with maintence free since there is an "Issue" that requires sealed batteries there.

I may, some day, fix that issue, and if I do I'll go GC-2 in that box too.

[Jon Mopar]

I didn't realize they were sealed....meh, I'm not a battery guy. I am running the 6Vx2 setup and it serves me well.

[Ramblin]

I agree. I just replaced the Trojan T105's that were 10 years old and original to my coach, not because they were giving me any problems, just because they were old, and I was about to go boondocking for a week and couldn't afford any surprises. I put them in my horse trailer, where they continue to perform just fine.

The new batteries were Costco's 6V golf car batteries ($70/ea) and were physically identical to the Trojans that came out but for the color. The battery cases looked like they came out of the same mold.

My advice: First, do the work to be sure your charging system is working properly, and that you don't have any phantom loads running your batteries down. Take the AGMs and have them tested. If they're bad, replace them with a pair of good quality flooded wet cell golf car batteries (like the Trojan 105s), and commit to doing the (tiny bit of) maintenance that wet cell batteries require. They will give you the best bang for the buck over the long haul both monitarily, and performance wise.