Do you occasionally disassemble your battery bank and charge individually?

[RickP]

Last year, I built a dolly type portable system with 4 BattleBorn 12V LiFeP04 batteries in 2S2P configuration for 24V. It is charged by a Victron 250|100 SCC most of the time, or a Victron 24/3000/120-70 inverter/charger if we happen to run low on available sun. It’s been running quite happily for a year, keeping a refrigerator/freezer and an upright freezer powered when not needed in its emergency power role.

I can’t find the reference now, but I recall reading that it is beneficial to occasionally disconnect your battery bank and charge the batteries individually to assure they are balanced. I was very careful to make sure every connection in the series pair used exactly the same length of the same cable in the hookup, so both pairs are seeing the load equally.

Any opinions or suggestions? I did speak with BattleBorn, and they say it’s not a bad idea to do this, so I’m leaning that way. I’ll need to get something to charge them with, as the Victron charger is 24V. I’m just looking for the experience and insight of this group and, of course, to extend the life of some great batteries.

 

[Short_Shot]

While it's not a *bad* idea, I don't see how it's going to be of any significant benefit.

 

[RickP]

While it's not a *bad* idea, I don't see how it's going to be of any significant benefit.

That was my initial impression, as he wasn’t saying “yes, you have to do this“ but if I gain anything useful (as in worth the cost of buying a decent charger) I don’t mind. If there is no real benefit to a system humming along with no issues at all, then I sure have other projects to do!

 

[Bob B]

I don't have batteries in parallel ..... but it seems to me like the best way to keep them equally charged is for them to be in parallel ... like they already are.
Seems like charging them independently would leave more room for unequal charge.

I would probably make sure I had some sort of monitoring capability to know if one pack started seeing more current than the other.

 

[chrisski]

My initial thought after having worked all day on a new system, is I spent so much work putting this thing together, I have to be able to enjoy it without taking it apart every year. It was 100 degrees in my garage as I was assembling my solar milk crate generator for 8 hours today, which is the same thing I've done the three days prior. There's balancers if this is a problem.

I think most importantly for four batteries in parallel is how you hook them up to keep them in balance. I have a document in my signature block about that.

 

[ArthurEld]

Most BMSs balance the cells. My personal opinion is that you are likely to do more harm than good taking your battery apart unnecessarily.

 

[Short_Shot]

That was my initial impression, as he wasn’t saying “yes, you have to do this“ but if I gain anything useful (as in worth the cost of buying a decent charger) I don’t mind. If there is no real benefit to a system humming along with no issues at all, then I sure have other projects to do!

But that's the thing.

Pros:
Can't hurt.
You feel better about yourself.

Cons:
You spent money you didn't need to spend.
You wasted time you didn't need to waste.

 

[RickP]

My initial thought after having worked all day on a new system, is I spent so much work putting this thing together, I have to be able to enjoy it without taking it apart every year. It was 100 degrees in my garage as I was assembling my solar milk crate generator for 8 hours today, which is the same thing I've done the three days prior. There's balancers if this is a problem.

I think most importantly for four batteries in parallel is how you hook them up to keep them in balance. I have a document in my signature block about that.

Read through the Paralleling doc, and with my series pairs paralleled together, I’m as close as I can be to perfect. Thanks for sharing!

 

[time2roll]

But that's the thing.

Pros:
Can't hurt.
You feel better about yourself.

Cons:
You spent money you didn't need to spend.
You wasted time you didn't need to waste.

If it is working fine.... reassembly does have some risk. Poor connections can be made inadvertently and possibly some other random mishap. Plenty of troubled examples are posted every few weeks.

Cell balance can be verified without tear down. Load it up and hit it with a temperature gun to verify all is running cool. Done.

Maybe run it top to bottom and log the capacity for reference.

 

[LithiumGuy]

I would say chances of mishaps like short-outs from tools and inadvertent loose connections are a BIG con. Then again, this is 2p2p so only 4 cells? That's not many cells. A lot of DIY setups have 16 or 32 cells then that's more risk of something going bad.

Why disassemble when you can use alligator clips for the series portion of your cells? Also, since you are using 2s2p configuration, after you individually charge each cell series, the cells connected in parallel will immediately equalize and self balance out.

So really the only benefit is you might be able to find out which cells in a parallel group are bad. Because they would otherwise be masked by being in parallel. That is, a bad cell in a parallel group of good cells can't be detected by a balancer since they act as one aggregate cell with the capacity and internal resistances add up or averaged out.

 

[Substrate]

RickP - the reference you are seeing is most commonly done with lead-acid - sealed VRLA AGM and Gels.

Normally a lead-acid bank does not use any sort of bms, and charging each battery individually before placing them into normal series / parallel service - and possibly every year thereafter is beneficial if one has the time and gumption.

The tendency among most folks is to just slap together lead-acid batteries of differing states of charge together, and apply a charger and then wonder why some of the cells are buckling or venting.

Charging them individually at the outset helps ensure that all the cells when placed into service are fully charged and balanced, (by the natural sealed recombination technique) so that they don't blow their tops from the normal series/parallel charge routine.

Owners should check their banks periodically that no battery measures more than 0.1V higher or lower at the terminals than it's neighbor. If it is, there may be high-resistance wiring infrastructure problem, or an impending imbalance condition developing.

You can fix the wiring issues easy enough if detectable, but if you have perhaps lower-quality batteries, then charging each individually say once a year will help any laggard cells finish the recombination and become balanced with the rest until next time you do it.

 

[RickP]

I should re-emphasize that these are 4 BattleBorn 12V LiFeP04 batteries, and not individual cells joined to form a battery bank. They were all fully charged and balanced to the same voltage before being put into series pairs to get 24V, then paralleled with exactly matching cable lengths to avoid cable-induced differences between the two pairs.

The groups of individual cells are contained inside each battery, and are monitored and balanced by the BattleBorn BMS inside each of the 4 sealed units, so I have no access to the individual cells. I’m only referring to disconnecting the main cables from each of 4 batteries and charging them individually.

Here is a picture of the components during construction of the system:

 

[time2roll]

I still see no reason to disassemble. Give it a check and record full capacity for reference.

 

[RCinFLA]

Stripping bolts, shorting out terminals, or breaking something vs. just assuring charging and balancing done properly.

Couple of important things you can do and they don't require dissassembly.

Get a clip on DC ampmeter and check parallel strings for current distribution with moderate inverter load. Better than 20% difference is okay, Better than 10% difference is great. Keeping track of this becomes very important if you place heavy inverter loads on system. Don't want one parallel string to get too close to max discharge current for battery. If your inverter load exceeds capability of one parallel string regularly it is better to put current monitor shunts on each parallel leg. If any one battery's BMS cuts out for any reason the other parallel string will take up full load. You need to know if this happens to avoid too much current drain on one string.

At least periodically, ensure you charge to a high enough absorb voltage for long enough time to give BMS's a chance to balance out cells.

A cell balance dump doesn't start until it gets above 3.4v so for 24v system that is 27.2v average. To get any balancing time better to absorb to at least 3.50v to 3.55v per cell, or 28.0v to 28.4v. They only bleed 100 mA or 200 mA per cell level (30 x 3.4AH cells in parallel in 100 AH Battleborn) so they need some time to pull a percent or two of AH capacity state of charge mismatch. If you can do this at lower charge rate it will give more time for balancing before charger shuts down charging for full state of charge.

 

[RickP]

Stripping bolts, shorting out terminals, or breaking something vs. just assuring charging and balancing done properly.

Couple of important things you can do and they don't require dissassembly.

Get a clip on DC ampmeter and check parallel strings for current distribution with moderate inverter load. Better than 20% difference is okay, Better than 10% difference is great. Keeping track of this becomes very important if you place heavy inverter loads on system. Don't want one parallel string to get too close to max discharge current for battery. If your inverter load exceeds capability of one parallel string regularly it is better to put current monitor shunts on each parallel leg. If any one battery's BMS cuts out for any reason the other parallel string will take up full load. You need to know if this happens to avoid too much current drain on one string.

At least periodically, ensure you charge to a high enough absorb voltage for long enough time to give BMS's a chance to balance out cells.

A cell balance dump doesn't start until it gets above 3.4v so for 24v system that is 27.2v average. To get any balancing time better to absorb to at least 3.50v to 3.55v per cell, or 28.0v to 28.4v. They only bleed 100 mA or 200 mA per cell level (30 x 3.4AH cells in parallel in 100 AH Battleborn) so they need some time to pull a percent or two of AH capacity state of charge mismatch. If you can do this at lower charge rate it will give more time for balancing before charger shuts down charging for full state of charge.

Great suggestions! Thanks, I’ll check those settings on the charger.