The world is awash with fancy lithium batteries. Here we will dig them out of a retired laptop battery.
This is another quick and dirty 'ible.
Here's the two line version:
Cells with less than 2v in them are pretty much dead.
Screwing around with lithium batteries can result in fiery disaster.
There are much more comprehensive guides to laptop battery salvage over at www.endless-sphere.com/forums.
Step 1: Gather Materials
I get dead laptop batteries from a small mom'pop computer repair shop. It's worth asking the repair tech at larger stores but sometimes they have silly company policies against being nice so be prepared to hear no.
Also you will need
Multimeter or voltage meter.
Step 2: Like Gutting a Plastic Fish
Poke in near the charge port. You want to pry open the seam without stabbing the batteries. The battery management system is in this region so you can stab that instead. Be careful with that knife.
The goal here is to get the case open without wrecking the cells or yourself. This is easier said than done since the case is usually glued shut.
Step 3: Hack Hack
Usually you will find several pairs of 18650 cylindrical cells. I like to keep them in pairs. Chop the battery pairs off from each other and from the battery management board.
Be careful not to rip the solder tabs off the ends of the cells. You'll want them intact and they are lightly spot welded on.
There is probably a nice way to salvage the battery management system but I just save the thermistors and toss the rest.
Step 4: Test the Cells
There's usually one pair of cells that are way lower voltage than the others. You might be able to wring a little bit of life out of these but MARK THEM AS IFFY.
Good cells will have about 3 volts or more. Cells with less than 2 volts are probably ready to be recycled.
The other cells are pretty much good to go. Jam them on your lithium charger and think up something creative to run with your new batteries. I made a monster electric skateboard.
Also be warned that it is potentially dangerous to mix and match old lithium batteries. They can burn like crazy if mistreated (eg. punctured, shortcircuited, overcharged...) and release poisonous acidic smoke so please bear this in mind.
Have fun and wear protection.
Step 5: Closing Thoughts
The cells all have solder tabs on them. These are great. They make for easy soldering and prevent excessive soldering heat from damaging the chemicals inside. Generally soldering directly to the bare ends of a cell is not recommended.
That said, my skateboard rattled its solder tabs off. I just cranked my iron up all the way and soldered right onto the cell ends. It's not the best way to do things but it has worked ok for me… thus far.