Replacing house batteries in our new motorhome with AGM

"Floating" or "standby use" suggests no activity. Rv converters that do 14.4, 13.6, and 13.2 have their 13.6 for camping when on shore power with some activity, and use the 13.2 for "storage"

On solar with flooded batts, once batts were true full early afternoon, I tried 13.2 but as soon as any small load came on, the Trimetric showed negative amps until the system stabilized at 13.2 again. With it set at 13.6, it held. I figured from that, converters have their 13.6 for the same reason.

Battery specs do not seem to cover for "after the absorption stage when you are still camping".

I've found that loads on my DC system while floating my 13.6v spec'd AGM require slightly higher voltages, the higher the dc loads the higher the float voltaeg needed to be ot prevent slightly discharging the AGM. The goosing of voltage to 14.7 reveals a slight discharge happens when floating at 13.6v with loads on the system.

Also colder battery means bump it up even higher.

Another reason I have contempt for fixed voltage converters or chargers, but ignorance was surely blissful.

landyacht318 wrote:
The ONLY AGm manufacturer I am aware of that specs a float voltage lower than 13.6v at 77f is Lifeline/Concorde.

Even with different charging voltage specs. My 250 is 14.1 to 14.4 "cycle use", but 13.5 to 13.8 "standby use"; while my 100s are 14.5 to 14.9, but 13.6 to 13.8 "float use"

I recharge them to full separately, but float them banked. On solar with them banked ( cyclic use) I leave the controller at 14.5

The ONLY AGm manufacturer I am aware of that specs a float voltage lower than 13.6v at 77f is Lifeline/Concorde.

mark52 wrote:
The house batteries in our new motorhome need to power a 2000w inverter and allow us to boondock for several days at a time. Against our better wishes, it cam furnished with a full size residential refrigerator that must be kept going while in the boonies. It came furnished with 4 6v Harris Professional Plus golf cart batteries. I think that the dealer let them discharge badly before the motorhome was sold to us. Anyway, time for new ones! After a little research and some prodding from a local dealer where we are having our warrantee work done, they are recommending 4 new Centennial CB6-250 GC2H sealed lead acid AGM Batteries. They seem pretty top notch when looking at the specs. 250 AH @20 Hr rate, reserve capacity of 570 min @25 amp draw. I can get them locally for $320 each + 30 core charge. Has anyone used these batteries or anything similar? Any thoughts? Thanks!!

I use a couple of these batteries ganged together in balanced-parallel in our RV ... if I could fit them, I'd use more. They're popular in the marine world, have a long warranty, and - unlike many AGM batteries - have a higher recommended float voltage of 13.6 volts - unlike the usual 13.2 volts of most liguid and AGM lead acid batteries. (I needed a higher float voltage AGM to exactly match the nominal voltage of our RV's converter):
http://www.fullriverbattery.com/product/batteries/DC115-12

mark52 wrote:
After more and more research on AGM batteries I became less and less impressed them.

You have been lead astray but it's too late now.

Nobody here said that there is any miracle involved with AGM batteries. Outlandish claims for ANY product should be suspect.

The fact is that AGMs are slightly better than conventional wet cell batteries IN ALL RESPECTS. They are sturdier, harder to damage electrically and typically last longer. But for many folks, the slight advantages are not worth the extra cost.

You have made a good choice for batteries.
But there is no need to denigrate AGMs in the process.
That is not justified.

Quick search. apex battery.com Shipping calculated to NW WA. 4 Batteries $1,075.40, shipping 175.20 = $1,250.60 or $312.53 ea. No TAX or Core. You could sell your 4 to a recycler.

Some AGMS can indeed safely accept huge charging amps, upto about 80% state of charge, but that last 20% still takes 3.5 hours minimum. the whole 5x faster was never a believeable claim. When AGMS were first brought to mass market they were said to be immune to sulfation. Perhaps thats when the 5x faster claim came out too and the marketers were staining their shorts at the potential profits of their fables.

Many cheaper AGMS say to limit charging amps to 30% of capacity.

Only a few like Lifeline, Northstar, and Odyssey say there is No changing amperage limit, as long as voltage is not allowed past ~14.7v. Lifeline says no LEss than 20% and that more is better. Odyssey says no less than 40% when deeply cycled. My Northstar responds wonderfully to high amperage from a well depleted state, and it is now over 1000 deep cycles and 5 years of age.

When new I could get it fully charged in about 4.5 hours from well less than 50% charged with 65+ amps available, NOw it takes nearly 4.5 hours to get from 80% to 100% when held at 14.7v

AGMs on regular automotive forums, are now seemingly thought of as a far superior battery, and as usual low price sells, and manufacturers respond with the cheapest product they can make which is still AGM.

I doubt these starter specific AGMS last any longer underhood as starting batteries, but at least the terminals will not corrode as fast and the letters AGM give warm and fuzzies and perhaps bragging rights to those that do not need them

Update:
I went ahead and made my purchase. After more and more research on AGM batteries I became less and less impressed them. It seems that a lot of the claims about what they can do have been disproven. I would REALLY love to have a battery that charges up to 5 times faster, but I don't think that that exists unless you spend A LOT of money. In fact, the battery dealer that I bought my batteries from confirmed that AGM batteries have a hard time recovering from a deep loss of charge and can actually take longer than a flooded type battery to charge. My purchase was 4 new Trojan T-145 flooded batteries. Ive had Trojan batteries in our last two motorhomes and they have always worked great. Hopefully these T-145's can handle all the fancy equipment in our new coach.
Interesting note - I don't know if its true but the T-105 may have approximately twice the life span than the T-145 and is a very nice battery. I felt it more important to have the 260 AH @ 20 hour rate from the T-145 in my case though.
Thanks for everyone's input!!

mark52 wrote:

time2roll wrote:
I assume the 2000w inverter will charge at 80+ amps and should be adequate.

I need to look into what rate my inverter will charge at over this weekend. If it charges at the right rate, It seems that one big advantage over flooded batteries is the AGM charges up to 5 times faster. This would mean a lot less generator time while dry camping I hope.

Inverters don't charge anything. If it is an inverter/charger, the charger part does. Also you only charge up to 80 or 90% SOC on generator. After that it is too slow for gen time. Solar or shore power for the 90-100%

The "5 times faster claim" was discussed on here recently, and debunked. For practical purposes, assume about the same times for your 50-90s.

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29796540/srt/pa/pging/1.cfm