Rebuilding a battery pack - Page 1
Forum section: electronics / beginners

author: Mr Lee
author_rank: Newbie
timestamp: June 07, 2025, 04:19:10 pm
content: Hello all. New to the site. I am trying to rebuild a battery pack for a cordless chainsaw. I have the new cells already but there is a silvery conductive material which links the cells together and I don’t know what it’s called or where to buy it. I will post a photo.This is for a 40 volt battery if that matters. Thanks in advance

author: pcprogrammer
author_rank: Super Contributor
timestamp: June 07, 2025, 05:50:50 pm
content: What you are looking for is nickel strips. See below link for search on Aliexpress.https://www.aliexpress.com/w/wholesale-nickel-strip.html?spm=a2g0o.home.search.0But be aware that you can't solder these onto a lithium ion battery. You need a spot welder to get the job done. Soldering to a lithium ion battery is dangerous because it can overheat the battery possibly leading to explosion and fire.Spot welding these strips to those batteries is also not easy and takes attention not to burn holes into the battery, especially on the negative terminal.You can find the tools for this also on Aliexpress.https://www.aliexpress.com/w/wholesale-spot-welder-module-18650.html?spm=a2g0o.productlist.auto_suggest.8.7531saMCsaMCvF

author: Mr Lee
author_rank: Newbie
timestamp: June 07, 2025, 06:23:09 pm
content: Thanks for the info! I couldn’t figure out what they were.If I need to, can I just use some copper (roof flashing) that i have?And yes these were spot welded on and thats why some got damaged when removing, but i actually was able to get one soldered back on so far. But i had to scuff the surface of the battery cell with some sandpaper first, and then the solder stuck. It only gets hot for a brief moment so I will take my chances but thanks for the warning. Plus, I saw a guy on you tube do it. Haha. 🤷🏻‍♂️

author: pcprogrammer
author_rank: Super Contributor
timestamp: June 07, 2025, 06:52:10 pm
content: Quote from: Mr Lee on June 07, 2025, 06:23:09 pmYes copper will work too.If you saw a guy jump from a really high bridge on Youtube would you do that too?Soldering a lithium ion battery often won't be a big problem, apart from possible degrading of the battery, but it can go wrong and in such a case it is a real bitch to put out the fire.Also make sure not to cause a short, because the internal resistance of these batteries is low and currents will be high and hardly limited. Temperatures rise quickly and it can go boom. These batteries are very different from the good old NiCad or MiHm batteries, so be careful.

author: Mr Lee
author_rank: Newbie
timestamp: June 07, 2025, 09:14:52 pm
content: I appreciate the warning. Wouldn't want it to go boom, especially in my face.I do have another question though. When I was disassembling the battery pack, I had to heat up the solder where these nickel strips connected to the circuit board, and when I did, this little square contact patch loosened and came off of the circuit board. Is this repairable?

author: pcprogrammer
author_rank: Super Contributor
timestamp: June 08, 2025, 06:27:56 am
content: Yes that is repairable. You can solder a wire to the capacitor next to IC2 to which the pad seems to be connected. Maybe the pad itself still has some copper and can be resoldered, but that is hard to tell from the picture.