Dell XX326 11.1V 60Wh Battery Pack Teardown

I picked up a lot of ten Dell XX326 6-cell 60Wh battery packs from an eBay seller for about $4.50/pack. The seller described them as untested surplus, and based on the presence of unworn external labels in the photos on the listing, I thought they might be unused packs and hoped I could turn around and sell them individually for a profit.

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No such luck. The packs had more physical wear than I expected. When I hooked them up to PackProbe, I only got data out of two of them without hassle and the data they provided seemed to have problems, for example, reporting design capacity as 0. With a little work, I got one more to spill its secrets. A couple more would ACK a query at their address, but that was it, and the rest gave nothing at all.

I decided to tear apart a few of them. When I got one of them open and measured with a multimeter, I found all the cells were flat, 0V. The next one was a little better, but not great.IMG_6764

3.18V, for 3 banks in series. Not looking good. Lets see what the individual banks registered.

IMG_6765Hmm, one bank measures 2.86V. That’s not bad. The other two banks must be junk though, with a combined voltage of less than 0.4V.

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Wait a second, 3.0V that’s not bad, hmmm…

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Yikes!!! One bank of cells has reversed polarity, in a really big way. I double checked my connections, but I still got the same result, -2.69V!

I tore into another 6 packs. One was nearly flat, with each bank just over 0v. The rest had at least one bank of cells at a reasonable voltage, with the remaining cells being low, flat, or slightly reversed.

It looks like all the packs are ~4-5 years old, and the packs I could get data out of each reported less than 40 cycles. I have to wonder what happened to these packs that they are in such crummy shape, or if the problem is with the pack design/engineering. There are also some manufacturing issues, I think two of the packs had welds break loose, without tearing the nickel conductor strips.

After pulling the individual cells out of three of the packs I’ve opened I’m even more baffled. All of them had at least one cell with failed spot welds. The first pack had all 0v cells, as expected. The second I thought would have two good cells, but it turned out only one cell in the bank was good. The other was flat. The third I thought had two good banks, but once the cells were separated, only one in each of those pairs was good. I think bad connections may have played some role in cell failures.

One theory: Cells paired with poorly connected cells failed because they were overused. I also wonder if some cells may have broken internal connections.

I’m holding off ripping apart the rest of the packs I’ve already opened, because I’m curious if I can get the battery management circuit to give up some data.

 

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