I got a bunch of Thinkpad Lithium Ion battery packs yesterday and dumped pack data out of all of them. The new packs had the same issue I saw with a pack for a different module, they don’t report individual cell voltages in response to commands that work with many other packs.
I did some research and found that the linux tm-smapi module provides access to individual cell voltages but from a little reading, it looks like this information may come by way of an embedded system controller. I figured there was still a good chance that this information was originally gathered from the battery via SMBus, so I wrote a simple arduino sketch to scan through a wide range of SMBus commands and look at the data returned. Unfortunately, I don’t see any values that look like cell voltages.
With any luck, the data is still there, and just packed in a way that isn’t obvious. I think I’m going to need to collect data from multiple packs to see which values differ, particularly if I charge or discharge the packs. The worst possible option is that reading the data requires putting the pack in an undocumented mode and using undocumented commands.
The Dell packs I have don’t yield individual cell voltages either, so while I was at it, I also looked to see if any of the Dell packs might report the data in response to non-standard commands. Again, nothing obvious. I couldn’t find any confimation on line that Dell makes this info available via any utilities, so I may be chasing something that isn’t there.
Note: There is a report that cells from this pack came out with a voltage of 1.7-1.9v. New cells at this level pre-charged at 50-100mAh for a few minutes until they reach 3v before charging can have a good useful life, but you should keep an eye on them during charging. They should get to 3v within 10 minutes or so, and shouldn’t heat up significantly during charging. Once charged, check the voltage after a few days and make sure they aren’t lower than 4.1v or so.
Over on Ebay, Red Planet Trading is selling Dell 9 cell, 80Wh, 7200mAh battery packs for $14.99 with free shipping. They currently show more than 10 available.
The pack is labeled that the cells are made in Korea, which means Samsung, of LG. Capacity is probably 2,400-2,500 mAh/cell.
This isn’t the pack to tear down if you are looking for high capacity cells, but at $1.66/cell and $0.19/Wh, its a good value.
Looks like the same pack is listed a few different ways:
I ordered one of these “Genuine Dell Battery Inspiron 13R N7010 N5010 N4010 9T48V M511R GK2X6” from eBay seller for $17.99 and free shipping. Its a 9 cell, 90Wh pack, which, I estimate, probably has 2,800 mAh cells. It arrived quickly and was packed well, but I haven’t opened it yet.
Works out to be $2/cell and $0.19/Wh, which is a pretty good deal.
There are a couple of downsides though. The pack I got had ~40 cycles on it. Not bad, but probably 10% of the lifespan. It wasn’t a surprise either, since the pack wasn’t described as new, it was listed as manufacturer refurbished.
Which brings me to the second problem. Before purchasing, I asked the seller for more information about what “manufacturer refurbished” meant and they didn’t reply. After purchasing and receiving the pack, and checking the cycle count, I decided that it would be worthwhile to get another couple of packs if I could get them at a lower price, so I took advantage of the “Make Offer” featured on the listing and offered a lower, but still reasonable price for two. They ignored the offer and let it expire.