How to rebuild a Li Ion laptop battery?

Question

I have an aging Gateway NX560XL laptop. The battery is toast and a new one, even aftermarket, starts at $130. So, to experiment, I began tearing apart the old battery to see what can be done. I found it used 8 standard size 18650 Li Ion cells arranged two cells parallel then in series (like: ====). Some online shopping revealed ~$7-13/ea replacements depending on mAh output. My plan is to load test to determine the bad cells and replace only those, as I read that typically only 1 or 2 may be bad.

I'm proficient with soldering, however these cells are attached with welded tabs. Some of them broke during disassembly and I'm not sure how to reattach them. What I found online are cells like these that have solder tabs pre-welded to the ends so I can solder wires onto.

Is there any guide available that provides the instructions and parts to do this kind of rebuild?

Answer 1

Typically, the batteries are connected to each other via spot welded tabs. You could solder wires to the batteries you found, but it might not fit afterwards. Make sure you use a wire with enough current carrying capacity (i.e. 14 AWG). Theses batteries do get hot and pass a lot of current during peak loads. You can also build yourself a spot welder rather cheaply if you want to try this route.

Make sure the case is well closed after your repair. Epoxy should do the trick.

There are a few tutorials on the web as well.

Answer 2

Beware: Soldering Li-ion cells can be somewhat dangerous, as when they get hot such as during soldering they can tend to explode.

Answer 3

Unless you have experience with electronics and soldering I wouldn't risk it. Batteries put together incorrectly have an unhealty disposition to extreme exothermic reactions (i.e. blow up) which can be quite fatal if you are close.

Answer 4

TL;DR version: Please don't try this at home.

About soldering: Soldering to Li-ion cells is very much not recommended. They can't take the high temperature. That's why spot welds are used.

Even without soldering, you are risking a battery fire.

You must NOT re-use old cells , even those that seem to test OK, in the same pack with new ones. Replace all the cells.

Rebuilders may test the cells they remove from old packs, but the "tested ok" cells do not get mixed with new ones in the rebuilt pack. Instead the cells that survive the first (superficial) tests are then tested very thoroughly to determine their useful capacity, voltage characteristics, etc. The rebuilder then combines them with cells that gave similar measurements to make up entire packs out of well-matched cells. Usually such packs include cells from several different "donor" packs. Then the pack is tested extensively before being sold.

As you can tell, it is a time-consuming process. (The testing of cells can at least be semi-automated.) Re-using cells from bad packs doesn't really make much sense unless are rebuilding a lot of bad packs. You are unlikely to get many well-matched sets otherwise.

At least.. all of the above is how the best rebuilders do it, and how it should be done. Li-ion battery fires, especially for a laptop-sized pack, are not anything you want to risk.