Discover AES LiFePO4 Battery with one dead cell- Is it possible to repair?

[208stephen]

I have a Discover AES 44-4800-3000 battery with less than 100 cycles that is showing one bad cell (0V) out of 16 (the rest are roughly 3.34V). I've had extensive conversations with Discover tech support and basically they are not set up to repair these and are very reluctant to offer much information or support for DIY repair. It's maddening and unacceptable to me that a virtually new $3,000+ battery is considered unrepairable. I did mange to find out that the cells are made up of 26650 3.2V 3.8aH cells- I think 16 in parallel. The battery case itself is steel and screwed together. I've opened up the case and located the bad cell by voltage testing, but that's as far as I've gotten. Any advice, experience, guidance would be much appreciated. I'm located in the Bay Area and would be open to paying someone to repair it. Many thanks

 

[sunshine_eggo]

Much like automobiles, they are built for ease of manufacture, not maintenance.

IMHO, that just sounds like a headache on every level.

Why aren't you pursuing replacement under warranty?

 

[BentleyJ]

According to the datasheet the battery is 16S15P configuration. So 57Ah divided by 15 cells corresponds to the stated 3.8Ah per 26650 cell. A quick search does confirm that 26650 LFP cells are available in 3800mAh capacity.

Something doesn't make sense. How does 1 cell go bad when its composed of 15 pieces? If one shorted out and took the rest down to 0V there would be quite a bit of heat. At the very least some discoloration of the PCB if not something more serious. Based on the pic one would assume voltage was measured at the M4 bolts on top of the PCB. Sounds more like a connection issue than a bad 15P cell.

 

[ScrotusGobbleBottom]

According to the datasheet the battery is 16S15P configuration. So 57Ah divided by 15 cells corresponds to the stated 3.8Ah per 26650 cell. A quick search does confirm that 26650 LFP cells are available in 3800mAh capacity.

Something doesn't make sense. How does 1 cell go bad when its composed of 15 pieces? If one shorted out and took the rest down to 0V there would be quite a bit of heat. At the very least some discoloration of the PCB if not something more serious. Based on the pic one would assume voltage was measured at the M4 bolts on top of the PCB. Sounds more like a connection issue than a bad 15P cell.

agreed,
connection or BMS?

 

[sunshine_eggo]

Something doesn't make sense. How does 1 cell go bad when its composed of 15 pieces? If one shorted out and took the rest down to 0V there would be quite a bit of heat. At the very least some discoloration of the PCB if not something more serious. Based on the pic one would assume voltage was measured at the M4 bolts on top of the PCB.

It depends on the nature of the failure. If the cell starts to lose its ability to hold a charge vs. dead shorting, it draws from the others at a rate that won't generate much heat, but can easily drain them in a day or two.

Sounds more like a connection issue than a bad 15P cell.

Certainly something to exclude first!

 

[ElectricIslander]

Warranty is 4 years or 10 Years if registered

 

[sunshine_eggo]

Warranty is 4 years or 10 Years if registered

@208stephen

No brainer. Insist on a warranty replacement rather than void any warranty left. Make them eat it.

 

[208stephen]

Thanks for all your response. Warranty is not an option for several reasons:
I'm not the original purchaser
According to the data logs the cell was having issues way back in 2/23 and then allowed to sit for almost a year (by the original purchaser)
I don't think the battery was officially registered by the original purchaser

Yes, voltage was measured at the M4 bolts. At cell 3 the voltage measured exactly the same as cell 2. And at cell 4 it was cell 2 plus 3.3V.

I haven't dug deep enough into the battery to see if there's any obvious damage or discoloration of individual cells. If it's a connection issue how would I evaluate that?

It seems unlikely to me that it is the BMS as it does seem to be operating properly. It's in low voltage vault which causes the battery to shut down after 120 seconds.

 

[BentleyJ]

Sounds like the main bus on the PCB is intact, somehow one of the connections from cell 3 up to the PCB/M4 bolt has failed. How hard is it to get access to the cells? Probably have to remove all the M4 bolts and lift the circuit board off.

 

[208stephen]

I think it's doable but I may have to remove the battery itself from the case. It looks like everything is bolted together.
Here's a screenshot of the diagnostics screen showing cell 3 with "1.000" Volts. According to Discover this is a default reading when the cell is really low and could actually mean that there's 0 Volts in the cell. Tech support that this was highly likely.

 

[BentleyJ]

You have verified Cell 3 is either 0 volts or is disconnected since it reads the same as Cell 2.

 

[208stephen]

Does anybody know if it's even possible to repair this battery? I'm surprised that with all the LiFePO4 batteries out there that there isn't someone offering repair service.

 

[BentleyJ]

I've had tool batteries repaired on ebay with good results but they are small and can be shipped easily. The Discovery battery is a bit out of the ordinary with the 15S configuration. If you can get the cell out of the enclosure it can most likely be repaired. 26650 cells are common, the bus straps are probably spot welded requiring some equipment for that process. There will be some kind of holder and/or connection method for + & - to the M4 bolts that go through the PCB.

I'd bet it can be repaired, just depends on how handy you are and if you have the time & tools.

 

[yabert]

Does anybody know if it's even possible to repair this battery?

Sure, open it!
We are always interested to see battery design, so please share details if you open it.

 

[208stephen]

OK. I appreciate the optimism. I'll dig into it and share my findings sometime in the next week or two.

 

[ElectricIslander]

All things can be done! Careful steps pay off

I fixed my suitcase welder which had to be totally disassembled to do it. Just put it on the dining table and put all the screws in egg-crates in order that they came out (so reassembly is just reverse order). I took lots of photos before pulling anything apart so I knew how it went back together. And labelled all cables that came out so it was obvious where to put back.

 

[208stephen]

I finally dug into this battery which wasn't terribly difficult. The outer metal case is screwed together and the lid comes off easily. There are 3 circuit boards that are exposed and can be unbolted and lifted off. Then there are a few more bolts that hold the main battery unit to the outer metal case. Once I could get at the main battery there are 4 long studs that hold together 4 plastic enclosures with large positive and negative busbars on each side that are spot-welded to the individual battery cells. There are 15 26650 (3.2V/3.8ah) cells in parallel and 4 of these per plastic enclosure, 16 in total in series. It looks like to open the plastic enclosure to get at the individual cells would require disrupting the spot welds of ALL the cells.

I have identified the dead string of 15 cells and each cell reads 0.0V. The rest of the cell groups in the battery all read in the range of 3.3V so it looks like it's this one group of cells that has caused the problem. I'm not really sure how this happened and despite having the logs, Discovery tech support has not been forthcoming on providing any info about the progression of events that might have caused this failure. In general, they've been entirely unsupportive of my efforts to repair this.

So the questions on the table for all you LiFePO4 experts are-

Is there any way to attempt to recover these cells? Or, once they read 0.0V are they DOA?
With the battery apart I can try charging the defective string of cells without involving the other cells or the BMS. I do have a bench DC power source with adjustable voltage and amperage.

Is there a technique using variable voltage and current settings that I might be able to inspire these cells to awaken? Or is it a lost cause?

 

[hwy17]

Or, once they read 0.0V are they DOA?

Finito.

 

[robbob2112]

I suppose having the original purchaser register and do warranty is out the window? or if it was never register pretend you are the original purchaser?

 

[ScrotusGobbleBottom]

Or, once they read 0.0V are they DOA?

Done, dead.

It is possible to feed them voltage but it could be very dangerous.
There is one or more cells in that group with an internal short that bled out the rest in that group. This could result in fire if you charge them.
If you dont find this cell(s) It is a hopeless project.

Your only option is to find an identical group (very unlikely)
Or spot weld your own group. Ideal it could fit back in the case

Or use it as a 15s battery. You would need to wire up a different BMS to do this. This could be beyond the scope of your comfort and experience.
I have built battery banks out of 18650s in the past and have a spot welder. Its not too terrible. You could never reuse those nickel buses tho. It will be destroyed if you try to remove the cells from it.

The problem with cheap spot welders is that they rarely have any way to have 3 deep as the welder part is fixed. You would need a spot welder that has a hand held welder.

You could perhaps look at Batteries Plus, I have heard they can repair power tool batteries. The same machine that can do that could most likely help you.