Hello all, my question is: What are the best way(s) to tell if an AGM battery has lost enough of its capacity that it should be replaced? (And if it's anything complicated I will probably need advice on how to do it.) Thanks for your help.(I should add that this is a group of 54 amp-hour CD Technologies Hi-Rate Max batteries that I have been using in parallel in the RV. I took them out and right now I have them in my house charging.)

Take it to Pep Boys and they will tell you. But better to have it checked by the authorized dealer of your battery brand.Mine went dead after 3 months. The dealer replaced it free even if I did not buy it from them. Most batteries have 3-year warranty.

https://batteryboss.org/shop/ups12-210mr-cd-vrla-battery/The 20 hr rate on a 54 AH battery is 2.7 amps. So a full battery ought to be at 50% SOC after 10 hours at 2.7 amps.So do them one at a time (in case some are good and others not so good while in your parallel bank)Find the voltage vs SOC table for those AGMs. EG, mine are 13v full and 12.4v at 50%. YMMV so find the right numbers.Charge each one to full, run a 3 amp load such as a typical RV two bulb lamp and check its voltage after 5 hours. (Disconnect the load and wait half an hour for the voltage to bounce back.) If the battery is as new, it should be about 75% SOC.If it is lower than that, you know the battery is not like new. Keep going, spot checking each hour from now on. Say it gets to your 50% voltage at 7 hours.That means your battery is only 70% good as new. 8 hours is 80% and so on.Now it is up to you how much capacity remaining is enough.

Hi,Were they wired in a balanced manner? How many are there?Are your batteries on this page?https://www.batterysharks.com/C-D-Technologies-s/1225.htm?gclid=Cj0KCQiAgebwBRDnARIsAE3eZjTl3PcFFDdmvKnHpE2uc-c68tyFsDaqEuLHnrVILdGNQSc-JzIJWFoaAm1EEALw_wcBSon of Norway wrote:Hello all, my question is: What are the best way(s) to tell if an AGM battery has lost enough of its capacity that it should be replaced? Hi (And if it's anything complicated I will probably need advice on how to do it.) Thanks for your help.(I should add that this is a group of 54 amp-hour CD Technologies Hi-Rate Max batteries that I have been using in parallel in the RV. I took them out and right now I have them in my house charging.)

If voltage is dropping to where you are not sure if the furnace can go all night.... time for new batteries.

They are the UPS12-210MR. Three batteries. They were pretty well balanced intially, but now they are within about 2/10ths of a volt. They date from 2010 and 2011. On our trip in November the resting voltage of the group was about 12.8 volts.

Deciding on Battery Replacement | Good Sam Community

Chum_lee
Explorer
Jan 14, 2020
2oldman wrote:
Son of Norway wrote:
They date from 2010 and 2011.
It's time.

I agree with this. If you have no diagnostic tools/skills and your battery bank won't power your system (from a known full charge) for more than a day, (or night) it's most likely time. At +-9-10 years of age, IMO, you have gotten your moneys worth, and a little more.

Chum lee
philh
Explorer II
Jan 14, 2020
theoldwizard1 wrote:
IMHO, you would be better off with a pair of 6V AGM golf cart batteries, like Trojan T105-AGM. Over 35% more stored power. Not cheap. You would have to order them through a golf cart distributor or solar power store.

Not cheap is an understatement.
River-Runner
Explorer
Jan 14, 2020
I just bought 4 Trojan T-105 AGM's from this www.onlinebatterysale.com source for a really good price. They were bought in December '19 and made in November '19.

They have automotive parts warehouses around the country where you pick them up. They had a Portland location, so worked well for me. Golf cart distributors/suppliers were much more expensive.
Veebyes
Explorer II
Jan 13, 2020
Sorry, missed the age of them. Yeah, it is time for replacement. Get whatever will fit in battery compartment. My preference is a single batter. Fewer connections to potentially give problems. A 4D will give close to the amperage of 2 6Vs. An 8D, if there is room, more.
theoldwizard1
Explorer II
Jan 12, 2020
IMHO, you would be better off with a pair of 6V AGM golf cart batteries, like Trojan T105-AGM. Over 35% more stored power. Not cheap. You would have to order them through a golf cart distributor or solar power store.
2oldman
Explorer II
Jan 12, 2020
Veebyes wrote:
How old are your AGMs?
Son of Norway wrote:
They date from 2010 and 2011.
Veebyes
Explorer II
Jan 12, 2020
Get one of these. https://www.amazon.com/OTC-3180-Battery-Load-Tester/dp/B000F5HU6C/ref=sr_1_11?crid=UXILT2AA3Z&keywords=battery+tester+automotive&qid=1578837992&sprefix=battery+test%2Caps%2C208&sr=8-11 Well worth th money.

How old are your AGMs? My last one, a 4D 215AH Lifeline, had a service life of 9 years.
covered_wagon
Explorer
Jan 12, 2020
time2roll wrote:
If voltage is dropping to where you are not sure if the furnace can go all night.... time for new batteries.

The simplest solution always seems to work the best.
pianotuna
Nomad III
Jan 12, 2020
For balancing an odd number of jars only method #3 works.

http://www.smartgauge.co.uk/batt_con.html

But the existing batteries have served their time--I would replace.
2oldman
Explorer II
Jan 11, 2020
Son of Norway wrote:
They date from 2010 and 2011.
It's time.