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[SOLVED] Ruined 2 12.8V LFP batteries by charging to 100% & leaving in garage

Finished charging, it took an indicated 153.68Ah on the Riden. A few minutes after, the pack measured @ 14.09V. I've buttoned it up and finished messing with this unit. It is now my best unit out of all 4 I have! All it took was a week of messing around with it ;)

Looks like spending an entire hot Texas summer in my garage stored at 100% SoC didn't affect it much.
Good job!
You are well on your way to grasping the understanding of this!
Some final thoughts:
Most of these batteries that are of reputable makers will generally have a >100% initial capacity vs rated.

It's most likely that your packs initially were never able to charge to 100% at cell level so there's not a baseline for comparison.

Total Wh should be = or > than Ah, and if not it would indicate there is an issue in your: battery, wiring or connections.
The nominal 12.8V (3.2V/cell) is a good value to use for calcs.
 
Finished in the middle of the night (while I was asleep), capacity.. 152.95Ah!
Wow! I’m excited and happy for you, @AC/DC ! Your discharge rate was a little lower, which might explain why it tested higher than nameplate. But still—awesome!

I have a bunch of 12.8V sealed batteries that I was using on a 12V system originally, then changed to 4S (4S4S?) when I switched to a 48v system.

I have a feeling that daily cycling will probably help ameliorate the balancing problem, but I really don’t want to find myself trying to cut open the sealed batteries to manually balance as you did. So I think I’ll be spending lots of time between 56.8 and 57.6 at very low charge current, say 1-2A. Together with an active balancer on all 12.8V units, I’m hoping it will be enough to stave off imbalance issues in the future.

I had been intentionally targeting lower charge voltages, hoping to extend their lifetime, but now I’m more concerned about balance than overcharging. Without a way to monitor the individual cell voltages (or actively balance them), seems prudent to give them every opportunity to passive balance, trusting the BMS to prevent overcharging of individual cells.

I presently have 4x brand new 280ah batteries that tested at 250ah. They all cut off charging before I can reach 13.8.

I’ll keep cycling them and charging with low current (<0.2A) to see if I can regain the missing capacity via passive balancing. They were bulging on delivery though, so I think my odds are a little lower than yours.
 
Good job!
Thanks!
It's most likely that your packs initially were never able to charge to 100% at cell level so there's not a baseline for comparison.
Completely true. I do have baselines for 3 other cells, one which sat & sweated with this one in the garage over the entire summer (the one that tested @ 137Ah about which I haven't yet done anything about), and two others which did not sit in the garage and just happened to test & 150Ah & 151Ah, respectively (the 151Ah one is the one which makes the strange noise which EW is replacing).

Wow! I’m excited and happy for you, @AC/DC ! Your discharge rate was a little lower, which might explain why it tested higher than nameplate. But still—awesome!
Yea, that is my max discharge with the tester I have, so it's nice & gentle on a 150Ah unit ;)
I presently have 4x brand new 280ah batteries that tested at 250ah. They all cut off charging before I can reach 13.8.
This is exactly what I was observing with this unit before I did everything I did with/to it and brought it back to 153Ah, not exactly at 13.8V but wasn't making it anywhere near my charging voltage. So this is a strong indicator of an imbalance, specifically with a high cell.
I’ll keep cycling them and charging with low current (<0.2A) to see if I can regain the missing capacity via passive balancing. They were bulging on delivery though, so I think my odds are a little lower than yours.
I recommend that you cut one open and manually balance like I did and see if you can get to 280Ah or at least close to it. If you do (once again, strong chance due to charging being cut off @ 13.8V), you can decide if you want to resurrect the other 3, if you don't, well, you have an underperforming battery which is cut but not a big deal IMHO. I'm assuming these are plastic cases, I lucked out with mine because they're easily-serviceable metal cases which look identical to new after putting back together. I would cut open the one that bulges the most to see what exactly happened inside. It will take a really long time with passive balancing as stated by others in this thread (very low max balancing current) and lead to potential uneven wear and tear on high & low cell(s).

For mine I'm planning to build a tool which attaches to the BMS balancing lead to do manual balancing, which then removes without any signs whatsoever. It would be specific to this kind of battery but may work on others.

Also, your packs likely use pouch cells too, you may think they're 4S inside but they're more than likely xP4S, unless you know they're using 280Ah prismatic cells (if they do, it will make manually balancing a breeze once you reach the posts).

Edit: resurrected battery reads 13.90V after sitting for 7 hours after full charge to 14.20V w/ termination down to 0.1A.
 
UPDATE: I created a tool for balancing these with minimal intrusion, all it requires is to remove any goop which may be on the balance lead before disconnecting it from BMS. I cut the wires in such a way that they cannot short by themselves, but care must be taken not to touch a conductive surface while tool is attached.

BalanceTool-1s.jpg

It's working great, I'm limiting charging to 0.90A which can take some time, but still overall it's quite efficient as usually there's only 1 or at most 2 cells which needs to be brought up, as I learned on 3 new battery units I've balanced this way. Funny enough, one unit which did have a low cell which took about 4Ah of charging this way tested at nearly 154Ah prior to being balanced! (150Ah advertised) You could probably charge at 1.0A or maybe even a bit higher, but I don't want to stress these thin wires (could only find an extension with 26AWG, whereas the battery's own leads are a lower gauge). Another brand new unit with a single cell which needed to be brought up took 8Ah!

Anyone trying to do this, this is my full protocol:
  1. Charge entire battery to 14.20V with termination down to 0.1A
  2. [Optional] Capacity test to BMS or 10.0V LVC, whichever happens first (BMS cutoff for me), then redo step 1
  3. Open battery, remove goop, disconnect balance lead, connect to tool
  4. Measure each cell. Typically you will have cells around 3.45V and then 1 or 2 in the 3.3xV range.
  5. Leave the 3.4xV cells alone!
  6. Charge <=3.40V cells to 3.55V with termination down to 0.10A. I use 0.90A max with this tool.
  7. Let sit for 6-12 hours, measure all cells. You should be good, if not do any topoff as needed. Don't sweat small differences.
  8. Disconnect tool, reconnect balance leads, measure that you get voltage at main battery terminals, screw cover back on.
  9. Enjoy your properly balanced battery!
  10. [Optional] Do another capacity test, then after charging to 14.2V w/ 0.10A termination, open battery up, connect tool and measure voltages.
 
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I recommend that you cut one open and manually balance like I did and see if you can get to 280Ah or at least close to it. If you do (once again, strong chance due to charging being cut off @ 13.8V), you can decide if you want to resurrect the other 3, if you don't, well, you have an underperforming battery which is cut but not a big deal IMHO.
While I'm not afraid to do it, I'd prefer not to, if it can be avoided. For now, I've just placed the batteries into service. They keep hitting OVP any time I get close to 100% SoC, but the voltage where that happens seems to be getting higher, so maybe they will eventually come into balance on their own.

I'm still seeking charging parameters I can employ to ensure a sealed 12.8V 4S LFP pack doesn't drift out of balance. With daily cycling experienced in a solar setup, and enough time spent at a high enough charging voltage, that ought to be attainable. It seems to be a good idea to cut charging current drastically as 100% SoC is approached, which ought to yield more time with BMS in passive balancing mode.

UPDATE: I created a tool for balancing these with minimal intrusion
This looks great, albeit a bit scary--I might not trust myself not to accidentally create a short somehow... and without an inline fuse, the balancing wire would become the fuse. :(

I feel conflicted about manually balancing these 12.8V batteries that are factory sealed. I hate waste, and would love to salvage something that otherwise would end up in a landfill. But I wouldn't want to have to repeated manually balance them, as it appears you're prepared to do.
 
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While I'm not afraid to do it, I'd prefer not to, if it can be avoided. For now, I've just placed the batteries into service. They keep hitting OVP any time I get close to 100% SoC, but the voltage where that happens seems to be getting higher, so maybe they will eventually come into balance on their own.

I'm still seeking charging parameters I can employ to ensure a sealed 12.8V 4S LFP pack doesn't drift out of balance. With daily cycling experienced in a solar setup, and enough time spent at a high enough charging voltage, that ought to be attainable. It seems to be a good idea to cut charging current drastically as 100% SoC is approached, which ought to yield more time with BMS in passive balancing mode.


This looks great, albeit a bit scary--I might not trust myself not to accidentally create a short somehow... and without an inline fuse, the balancing wire would become the fuse. :(

I feel conflicted about manually balancing these 12.8V batteries that are factory sealed. I hate waste, and would love to salvage something that otherwise would end up in a landfill. But I wouldn't want to have to repeated manually balance them, as it appears you're prepared to do.
My batteries are easily serviceable, the metal case's top is held in place by 10 screws and can easily be taken off, I think your main problem is that yours are basically a sealed plastic box which you would need to cut. I don't think the tool is that scary, it's a super quick disconnect so you can just disconnect it when not charging to be extra safe, and also just put some plastic (even saran wrap would work) over any metal parts of the battery where the tool might rest. The tool itself can't short out by itself due to how I cut the wires, unless you purposefully bend and touch the wires together. On the flip side, I really need to be careful because my battery is in a metal case, whereas yours is plastic so less to worry about. That plastic Amazon shipping envelope worked great tho, and I've done 3 separate units so far.

Were they my batteries, I'd def balance them properly prior to putting them in service — this is in essence what I'm doing with my own batteries. I'll be using them in series, the voltage is now very close between the two I'll use as a small 25.6V 150Ah backup system with a 2.5kW inverter, they're at 13.79V & 13.82V (the latter still has to settle as it had a balance on one of its cells today).
 

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