Battery discharge question

[GLC]

I have a 24 volt system that consist of 12 battle born 12 volt batteries. They are wired 2 in series and then 6 in parallele. For some reason, one battery in each series always discharges faster than the other. In other words, as batteries discharge, one batter in a series will be at 12.5 volts and the other will show 11.5 volts. This is consistent across the paraellel string. Thinking it was battery issue, I took the system down, recharged all batters to full and then repositioned all batteries putting the ones that stayed at a higher charge rate together and the ones that were at lower charge rate together. Still then same issue. One side of each series was still on a regular basis discharging faster than the other. I don.t understand why one side of a series always depletes faster than the other. And even when I move batteries around the same things happen even with different battery locations.

 

[BentleyJ]

The description is a little confusing. Did you mark the low and high batteries before moving them to keep track of them?

After the new series battery configuration is assembled and wired are you saying batteries that previously were high are now low? That doesn't make sense in a series string since there is only one electrical path and exactly the same number of coulombs have passed through both.

Moral of the story: Its better to use batteries of the same voltage as the inverter so they don't have to be connected in series. Parallel connections are fine as those are mostly self correcting because the low voltage battery will draw more current.

Maybe try a couple of these. https://www.victronenergy.com/batteries/battery-balancer

 

[GLC]

The description is a little confusing. Did you mark the low and high batteries before moving them to keep track of them?

After the new series battery configuration is assembled and wired are you saying batteries that previously were high are now low? That doesn't make sense in a series string since there is only one electrical path and exactly the same number of coulombs have passed through both.

Moral of the story: Its better to use batteries of the same voltage as the inverter so they don't have to be connected in series. Parallel connections are fine as those are mostly self correcting because the low voltage battery will draw more current.

Maybe try a couple of these. https://www.victronenergy.com/batteries/battery-balancer

Did you mark the low and high batteries before moving them to keep track of them?
Yes
After the new series battery configuration is assembled and wired are you saying batteries that previously were high are now low?
Yes

 

[12VoltInstalls]

Did you mark the low and high batteries before moving them to keep track of them?
Yes
After the new series battery configuration is assembled and wired are you saying batteries that previously were high are now low?
Yes

You need to crisscross your cables to balance the loading and charging better is my guess.

 

[Mattb4]

Can you provide an image of how they are connected?

 

[GLC]

You need to crisscross your cables to balance the loading and charging better is my guess.

Weird thing is that not all batteries are on the same side that discharges low. It is random from side to side.

 

[GLC]

Can you provide an image of how they are connected?

I will see if i can find a drawing somewhere on the internet but it is :
Plus to minus on two batteries creating a 24 volt series on two batteries. Six sets of these. Then these six sets wired parallele.

 

[MrSparkle]

You need to crisscross your cables to balance the loading and charging better is my guess.

That would fit in case of parallel. (Diagonal connection of parallel.)

The problem described within series-sets.
"One side of each series was still on a regular basis discharging faster than the other."

@GLC
As per Matt's request, provide photos so that we all can clearly see all the cables connecting all the individual cells terminals, so that we can get a better overview of the whole setup.

My guess the problem might be due to inconsistent connections and/or different resistance between different buss bars?

 

[12VoltInstalls]

Plus to minus on two batteries creating a 24 volt series on two batteries. Six sets of these. Then these six sets wired parallele

That would fit in case of parallel. (Diagonal connection of parallel.)

I can imagine this parallel group of series pairing being suboptimally cabled.

As per Matt's request, provide photos so that we all can clearly see all the cables connecting all the individual cells terminals, so that we can get a better overview of the whole setup

 

[MrSparkle]

I can imagine this parallel group of series pairing being suboptimally cabled.

I agree. If the parallel part of setup is not connected diagonally, that also creates a problem. Hence why photos would be valuable so that we can clearly se how all the connections are made between all terminals, both series sets and parallel sets.

 

[mikefitz]

. I don.t understand why one side of a series always depletes faster than the other.

Since they are in series they deliver current at an equal rate, they deplete at the same rate, but the battery capacities are not equal, thus at a low capacity, they will show very different voltages.
There is some evidence that Battleborn batteries loose cell balance resulting in capacity loss . There have been issues with intermittent internal connection between cells and battery post
There can be an issue when charging 12v batteries in series that one will reach cell overvolts before the other, terminating the charge cycle early for that string.
What may help,
Measure the Ah capacity of each battery and also the post connection to confirm they are usable.
Add battery balancers/equilisers to each string.