My Thinkpad's battery life had gotten pathetic. When I first bought my R61i in April 2008, its 7 cells could endure 4 solid hours of continuous use before needing to be recharged. But after 22 months of heavy use, it could hold a charge for about 25 minutes. Lenovo sells replacement batteries for $143, but I found a seller on Amazon who was selling the same 9-cells listed on Lenovo's site for $45. My laptop's battery only has 7 cells, but I didn't process this before ordering.
The battery sat in the mailbox I never check for a week before I thought to check for it there. Sitting in a mailbox for a week in Fairbanks, Alaska in January probably wasn't great for the life of the battery, but thankfully lithium-ion electrolytes won't freeze above -40 C. After I got the battery, I finally noticed that it didn't fit in my Thinkpad R61i. Rather than return the battery, I decided it would be less hassle to figure out how to make this battery work than to return it.
Li-ion batteries are pretty dangerous, as it happens. Consumers should never open an Li-ion battery's protective case, but I did anyways. Note: this is very dangerous, and probably a bad idea. Knowing full well that Li-ion batteries can ignite or explode if mishandled or punctured, I very carefully opened the new battery I bought online with a pocket knife to see what was inside.
I first tried to make this new battery fit into my laptop's battery slot by trimming the plastic, but realized that the locking mechanism and dimensions couldn't be made to fit easily. Once I got the case apart, I was able to test that the new battery would work with my laptop by plugging in the short connector cord, fully expecting both the battery and my laptop to burst into a spectacular carmine blaze.
However, the new battery worked fine without so much as a beep or an entry in the system log. At this point I decided to replace my original laptop's innards with the guts of the new battery.
Getting the original 7-cell battery apart was much more difficult and time-consuming than the new 9-cell, but I finally succeeded and didn't break too much plastic in the process.
I was cautiously optimistic that I could just swap out the Li-ion cells directly, but the original battery had electronics around every cell. Probably these electronics are to keep the battery from exploding.
It was pretty obvious beforehand that not all the cells would fit in the original case. After removing the old cells, I removed excess plastic inside that was getting in the way and cut slots on the back so that 3 cells could just hang from the back of the case. Note: this is also probably a bad idea, since puncturing an Li-ion could cause it to ignite, and metal fires are serious business.
Those warnings aside, I covered everything in electrical tape, including some stripes to match the art on the back of my display, plugged in the frankensteinian battery, and it continues to work! At the time of this writing, it hasn't even exploded yet. I will update this post if/when it does ignite or explode, supposing I survive the incident. The TSA screeners will probably have some questions for me if I ever decide to board an airplane with this thing, but it probably looks just like any other laptop battery on an X-ray scanner.
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