I needed to get a 36 volt battery pack for my electric bicycle, to see about getting it back on the road. The bike is not important, though it's an Electra Townie I bought in the 00's, and it has a front wheel hub motor from e-BikeKit, also from the 00's, and a Cycle Analyst dashboard thing, also from the 00's.
On YouTube, I found this video from Jehu Garcia talking about scooter batteries. The Bird Scooter rental agency had changed hands, and decided to change their scooter platform, meaning they dumped the old Bird Scooters. Jehu got ahold of the battery packs from the dumped scooters, and has a zillion of these packs. He explained they're untested, and he's selling them for cheap, with a generous return policy. For more details, see: https://www.youtube.com/watch?v=bp1KjvT4nmQ
Bottom line is - these are 36 volt 10 amp-hour packs made from 18650 cells. There is a bundled BMS. The cost is $35 per pack. I thought, that's worth an experiment. It does not include a charger, and they sell chargers for another amount, but I have a charger that's lying around that could be used.
The pack uses a CT30 connector for discharge. There is another connector meant for charging, but you can use the CT30 connector for charging as well. I've never used CT30 connectors (or the other sizes), but a quick search on eBay turned up some connectors I could use to build adapter cables. My bicycle build used a connector typically used for trailers (in the USA).
I'll show pictures of everything first -- then later go over what was required to get it going.
This is the overall battery
The main set of connectors at one end. The pair that has red/black wires is the main connector, and it has a CT30 connector. The one with the green/white wires -- Jehu said that was for charging through the BMS -- it uses a different connector, which I don't know the name for it, neither do I have the connector. Jehu's video showed charging through the CT30 connector.
At the other end there's another connector - which I don't know what it does.
The battery itself is a plastic case, and at each corner there is a thingy where you can obviously use screws to mount it to the body of something like a scooter.
This is the information label. You see it's built by Ninebot, rated for 36 volts 280 Watt hour
Yeah, it's a small pack, not much capacity, but it'll get my bicycle on the road again.
This is the adapter I built to go from the battery to the wiring harness on my bicycle. The out of focus orange blob at the front is the CT30 connector.
Getting the battery running
First thing I did was check the voltage at the main connector. That was 2-3 volts - which made me worry that I'd need to test Jehu's generous return policy. But, his video went over a couple things to do to wake up the battery.
I rigged up a connector from the charger I have to connect with the battery. By the time I got to this, the CT30 connectors had arrived, and one of them was part of the adapter.
I connected the charger and at first it didn't seem to do anything. Jehu's video shows something on the BMS board that he claims is a reset switch. I poked a hole in the plastic and tried to press whatever was there, but it didn't seem to be any kind of switch. However, fairly quickly after poking around, the charging seemed to start going, with a red light blinking on and off. After a while of that, I checked the voltage and it had increased to the 35 volt range. And, after awhile longer, the light on my charger turned to green, other lights on the battery seemed okay, and the voltage read 43.7 volts. That's a full charge for a 36 volt Li-ION pack.
After that, I built a rough adapter to go to my bicycle, took it out, and the bicycle woke up perfectly. There's a number of things to do on the bike to make it road worthy, so all I did was make sure the dashboard worked, and the motor spins. All that was fine, which was a relief after not using this bicycle for several years.
The blue light you see in the pictures indicate the pack is in good condition.