My buddy brought me an electric bike. He said the battery was shot and the bike will no longer work. I just happen to have a 36v lithium battery that was on my old scooter and I no longer need it as I stripped that scooter and am piecing it out.
The funny part about this story is that my buddy brought me the bike at work. When he wheeled it into our office, my manager was in the room and we were having a meeting. My boss is cool and was laughing. (Being an "old-timer" now, most managers are half my age). I told him that I may be back, on my lunch break, to troubleshoot the bike. The boss is good with that as work is pretty slow right now. My buddy, that brought it in, gave a quick head nod as he left the room and said "I'll call you later, bro". We all chuckled.
While on my "lunchbreak", I got the bike and started to troubleshoot it to confirm his suspicion. When shooting trouble, it is important to get as much info from the user and duplicate the trouble. Measure twice, cut once. Confirm twice, fix once. This is the way.
With the bike all together, I try to turn it on and the display flickers only when you press the power button, then off. The bike does not turn on.
Unplugged his battery and measured 34v at the packs discharge port. OK, that is pretty low.
I reconnected his battery to the bike and plugged in his charger, the charging light never went red to indicate charging. Could it be the charger?
I measured the voltage at the end of the charger then checked the charging cable exiting the controller. Yep, I see charging voltage. Charger may be good. As well as the controller.
Then I checked polarity of my charger and the original charger. They are wired the same. YAY!
I plugged in my charger and still the battery would not take charge.
I double checked the polarity of his battery and it is, in fact, wired the same as mine.
I connected his charger into my battery. The charger light switched from green to red. His charger works.
Having removed his battery now, I plugged in my battery and the bike works. Throttle, PAS, lights, all work.
He is super stoked as this bike will be for his grandson. I just need to mount the new battery and the bike will be ready to roll.
I told my buddy that the battery may have sat for some time and has discharged to the point of no return. The BMS inside monitors the pack voltage and will halt charging when faults are detected, such as low voltage. He looked surprised (because he hadn't told me) and said that the bike had sat for almost a year before his son-in-law tried it and was sadly disappointed.