Yesterday, I'm building a DIY battery pack out of cells harvested from old laptops, thinking "Man, I wish I knew someone with an old broken e-bike or something".
Very next day. I go for my daily walk. 1 block from my house, e-scooter on the curb, with a sign that says "FREE". "Sold!" I said out loud, and carried the thing one-handed quickly back home (okay I only made it a few houses before I switched to two hands).
The escooter itself was held upright with zipties, rear wheel was present but not attached, rear tire was blown, and while it did power on and show something on the screen, the throttle didn't do anything, and it was physically sticky (and thus very dangerous). And e-scooters are banned in my town (my whole province really), and they're pretty dangerous, and I'm stupid enough to ride without a helmet, so I decided to scrap the scooter for batteries.
I found 30x DMEGC INR18650-26E, rated at 2600mAh at 0.5C, and rated for up to 3C discharge: https://e-foton.pl/userdata/public/assets/Testy_ogniw/DMEGC-INR18650-26E.pdf
I have no use for a 36v series battery pack or its BMS, so I pulled a single cell out of the nickel stripping and threw it in my tester, set for 2A discharge, 2A charge, 5 cycles, 10 minute rest period between:
https://i.imgur.com/egbT45Z.png
I got just over 2500mAh at 2C. Cell only rose ~3°C at end of discharge curve. Cell dropped from 4.1895v unloaded to 4.0250v under 2A, indicating internal DCIR 82.25mΩ. Datasheet states <25 mΩ(ACIR), but I don't have an ACIR tester, however these DCIR values are very good and well within the expected difference.
TLDR: Got free e-scooter batteries. All my testing indicates they are near-new, in perfect health, and quite safe. 280Wh of energy storage, enough to watch old TV episodes on my phone for the first few days of the American Invasion.
Honestly, sounds like a recipe for a house fire. I'm all for DIY solutions and I would love to work on a project like this for an old laptop of mine, but batteries is a line I avoid crossing. When they go up in flames, you're thoroughly fucked.
I used to feel the same way. BigCliveDotCom talked me into it a couple years ago. Battery chemistry has gotten way safer over the years, good chargers with protection circuits can be had for pennies, and the 18650's especially are in steel cans giving them a little bit of armor, and they often have a CID in one end (giving it a vent-like appearance) that will physically cut the circuit off via physics (not electronics) if pressure builds up. It's not 2016 anymore for lipos, that's for sure.
Then again you can also go the LiFePo4 route - those are becoming more easily available, and they're even safer, albeit about half the capacity.
Honestly, I had a battery from 2021 go up in smoke on me... And I hadn't even done anything with that, the manufacturer made a mistake somewhere. No spicy pillow as a warning, nothing. Even if something physical cuts off the power - if the chemical reaction has started, it's extremely difficult if not impossible to stop it.
I've certainly shorted a few batteries by accident and turned their wires into high current fuses a few times, which lets out a lot of smoke and a bit of glowing hot metal out of the wires, but I've never seen a battery itself do that in all my years. The key is to just work with them fully discharged, solder them to the charger, assemble it, THEN charge it.
https://www.youtube.com/watch?v=-Y23nfAOiXQ
Yeah you shouldn't if you don't know what you're doing. If you do on the other hand...