two batteries connected in series going out of whack

[New KID On The Block]

I am working with the seller of the batteries -- who in turn is supposedly working with the manufacturer -- on a warranty replacement. They're having me do some testing on my end.

At 8:44 pm, the two batteries showed A) 12.64v and B) 12.61v.
At 9:44 pm , the two batteries showed A) 12.54v and B) 12.51v.
At 10:44 pm, the two batteries showed A) 12.43v and B) 12.39v.
At 12:33 am, the two batteries showed A) 12.21v and B) 12.18v.
At 1:44 am, the two batteries showed A) 12.07v and B) 12.03v.

That is part of what I sent them. They were suppose to call me today but did not. I'll see if they call me tomorrow.....

The interesting thing is -- as can be seen in my results above -- even with lower voltage during ABSORB, the 'good' battery holds voltage better than the 'bad' battery under load.

Two batteries within 0.3volt of each other after several hours loading 

I think you will be darn lucky if the battery supplier entertains a warranty replacement as both these batteries look good to me.
If you are expecting dead on identical performance from two same model batteries from the same manufacturer (and even from the same manufactured batch) then I fear you are always going to be disappointed.

I recommend you forget this issue and only make  a warranty claim if one of the batteries fails

dgd

dgd, thanks for your input. The 0.03v difference after several hour loading isn't what worries me. It's the great divergence in voltage between the two batteries at the end of ABSORB. Neither batteries are absorbing properly. One is absorbing at 13.7v and the other absorbs between 14.7v to 15.2v, depending on what I set ABSORB to -- i.e. 28.5v to 29v. But I do appreciate the input about 0.03v not being a big deal.

On a more positive note, changing PV panel config to (2) parallel strings appears to have improved efficiency by quite a bit.

Previously, I've observed 435w as about the highest I've been able to obtain. Today, I saw the KID go as high as 536w at one point. I was able to snap a photo at 532w to document the milestone.  This is awesome! 536w definitely makes me smile. It does have to be noted that today's weather is cooler (lots of intermittent clouds) and a bit breezy so I think that is definitely helping to cool down the panels to produce at optimal output as well. 

[New KID On The Block]

Just an update...

It took a while working with the seller but finally today the manager gave the approval to send me 3 new 125Ah batteries for the price of 2. That part is not surprising as that's what I proposed. What did surprise me is that they're allowing me to just keep the 'bad' battery instead of shipping it back to them. Wow! That was unexpected.

But before I get too happy, I need to wait and see how the 3 new batteries perform. If they perform properly, connected in series-parallel into my battery bank, I'll be extremely happy with their customer service and warranty servicing.

So let's wait and see what happens.