unbalanced sla/agm bank .....

[Scot]

I do apologize, not really sure where to post this ...... what I've got is 8 pair of 100ah 12v sla/agm batterys connected as 24v.
My question is, I've decided to pull and run each through a desulfate cycle on my 12v charger, I pulled the first pair, cycled and charged each,
well, after completion and a 36 hour rest one battery shows 13v and the other is 12.8v .
I'm at a loss as to how to proceed. Should I pair "like voltaged" batteries when I reconnect, should I balance this pair with each other before reinstall ?
Any info would be greatly appreciated.
Thanks again .....and yeh.... I am a rookie
thanks guys

 

[sunshine_eggo]

First, SLA and AGM should never be equalized unless the manufacturer specifically publishes an equalizing voltage and process.

SLA and AGM are not necessarily the same either. AGM is a specific type of sealed VRLA battery and may behave differently from a SLA.

So to clarify, are these SLA, AGM or a mix of both... or are they all the same brand and type of battery?

If you're using some sort of "pulse" desulfator, that's probably fine. Just be aware it's likely not doing anything beneficial.

Elements of a series battery bank should be as identical as possible:

1) should be the same capacity.
2) should be the same internal resistance.
3) should lose charge at about the same rate.

When in series, it is critically important that they each reach peak 12V voltage when the system reaches peak 24V voltage. If they are significantly different, there's a good chance the higher voltage battery is being damaged.

Both of those voltages are consistent with a fully charged battery. It's hard to say if the 0.2V difference is meaningful.

If you have a battery load tester, it's probably worth seeing how they respond to a load using a separate volmeter to monitor start and end voltage. If you have a digital tester that can directly measure internal resistance, that's very valuable information. I'm a fan of the Ancel BST200. Any similar unit is useful on a comparative basis. Pairing batteries of the same capacity with similar internal resistance means both batteries will respond to a load/charge relatively evenly.

 

[Scot]

thank you much for the info ....
all the batteries are identical and are identified as "Sealed Lead Acid" "Absorbant Glass Mat" type.
I will check out the tester you mentioned and thanks again for the information.

 

[sunshine_eggo]

Cool. All AGM are SLA but not all SLA are AGM, so this simplifies it.

They are simply AGM

In the absence of any additional information, those batteries should never be charged above 14.8V. A desulfating equalization charger may take it higher than that. That would damage it.

If in series, it's critical that neither 12V be above 14.8V.