C/20 specs related to a battery bank

[off-grid-geeks]

Thanks in advance for your answers...

The manufacturer's specs for the 6 volt flooded batteries I am using in my battery bank states that the absorb stage should end at 3% of C/20. And for a standalone battery of theirs the 20 hour capacity is 208 amps. So, the 3% would be 6.24 amps.

My question is, does C/20 change depending on the battery bank configuration?
I am running a 2S4P configuration; 4 parallel strings of 2 batteries each. So while the 20 hour rating of each individual battery is 208 amps, and therefore each 2 battery series string is still 208 amps, the total bank has a capacity of 832 amps.

Is my 3% ending amps then based on 3% of 208 amps (6.24), or is it based on 3% of 832 amps (24.96) for the total bank?

I have used the search function for the past couple of hours, have read lots of posts, but did not find an answer.

[Vic]

Hi o-g-g,

YES,  you are correct.  For batteries/strings in parallel,  you should multiply the recommended EA value by the number of parallel battery strings.

The EA value for your battery bank depends on the Absorption voltage that is used.

Generally,  four parallel strings of batteries can be trouble.   Often there will be no problems noticed initially.  But,  in time,  as batteries age,  any string balance that was present initially,  changes  and one or two strings wind up getting charged fully,  and contribute during discharge.  The lagging strings get undercharged,  and have little to contribute on discharges.    In time the undercharged strings become damaged,  and are usually not recoverable.    Each cell of the battery bank ages a bit differently,  and parallel strings make these aging differences much more pronounced.

Batteries that are often tended and monitored do much better than do those that are ignored until "the lights go out"

As you probably also know,  great care needs to be taken in just how the parallel strings are wired to achieve the best possible balance.

Carefully monitor the SGs of each cell at least monthly. Label each battery and cell,  and record the data in your battery Logbook.

A DC Clamp Ammeter will be a great help in monitoring the string balance.
Just my opinions,     Vic