Deciding on Battery Replacement

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.

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

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_wcB

Son 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.)

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.

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.