I have fifteen 12V 150Ah flooded batteries in series as part of a 10kVA off-grid system. Every once in a while, I test individual battery voltages. I've noticed that a few of them are, regularly, lower than the rest. For example, here's a reading I took today (#1 thru #15):
12.18 12.23 12.29 12.17 12.07 12.17 12.15 12.27 12.24 12.21 12.08 12.17 12.03 12.23 12.15
As you can see, batteries #5, #11 and #13 are "behind" the rest. And, here's the average of about two dozen readings taken over a period of 18 months:
12.19 12.28 12.29 12.12 12.08 12.15 12.02 12.25 12.21 12.16 12.07 12.12 12.03 12.23 12.13
So, this is a chronic problem.
Btw, here's the battery voltage history.
I've tried "equalization" a number of times, but given the nature of off-grid systems and the lack of a suitable generator, equalization hasn't followed the typical protocol (raise individual battery voltage to 16.5, continue charging at 3-6 amps for 12 hrs) ... and it hasn't achieved much.
So, here's what I'd like to do: Using a 12V battery charger, charge each of #5, #11 and #13, in turn, while they are in use. The plan would be to run the charge between sun down and sun up, doing one battery each night.
Can someone point out the holes in this plan?
Also, can somebody answer the key question: is it technically sensible to charge a single battery within a bank of 15 while the bank is connected to the load? [My worry is the fact that the charger will be connected to 2 circuits; one, the battery being charged; the other, the rest of the batteries and the load ... in the reverse direction]. Some explanation of why or why not would be appreciated.