Help me understand how I fixed my battery please

Hammick

Member
Region
USA
I bought a bike with a Shark type battery. The battery would not wake up and the level meter on the battery showed nothing. Nothing I tired worked. The battery was reading 43.8 volts at the discharge terminals.

I read that it is possible to charge a Lion battery through the discharge terminals bypassing the BMS. So I hooked the charger up to the discharge terminals and charged the battery removed from the bike for a couple hours. Voltage was coming up nicely and got to about 52 volts. The battery would still not wake up. When I pressed the level meter on the battery it showed nothing.

So I went to hook the battery back up for more charging and I accidently put positive to negative and negative to positive. The charger made a popping noise and then a burning smell. Immediately after this mistake the level meter on the battery started working and showed full. The bike rides just fine so it appears reversing the polarity somehow fixed the BMS in the battery. My charger is fried but I can get a new one for $18.

Can anyone explain the logic to this? I would have expected this to fry the BMS also. But it appears accidently reversing the polarity brought my BMS back to life.
 
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PedalUma

Well-Known Member
Region
USA
Two days ago I purchased a Rattan LM500 from a furniture wholesaler on Craigslist. He had bought two of them new in unopened factory boxes during an auction. I got it home and was bummed that I could not get the bike to turn on. The battery would not wake up and the level meter on the battery showed noting. Nothing I tired worked. The battery was reading 43.8 volts at the discharge terminals but would drop to 24.2 volts when I turned the key on (I don't understand this as the Rattan bikes will run with the key in the off position).

I read that it is possible to charge a Lion battery through the discharge terminals bypassing the BMS. So I hooked the charger up to the discharge terminals and charged the battery removed from the bike for a couple hours. Voltage was coming up nicely and got to about 52 volts. The battery would still not wake up. When I pressed the level meter on the battery it showed nothing.

So I went to hook the battery back up for more charging and I accidently put positive to negative and negative to positive. The charger made a popping noise and smelt burnt. Immediately after this mistake the level meter on the battery started working and showed full. I popped the battery into the bike and was able to turn on the display. The bike rides just fine so it appears reversing the polarity somehow fixed the BMS in the battery. My charger is fried but I can get a new one for $18 instead of $400 for a new battery.

Can anyone explain the logic to this? I would have expected this to fry the BMS also. But it appears accidently reversing the polarity brought my BMS back to life.
Nope. No explanations. You must have supernatural powers watching over you to be thankful toward. Make burnt offerings to Zeus, god of lightning? The whole battery could have discharged the entirety of its stored energy in 1/10th of a second burning everything around it in a flash chemical fire. Let's say Luck. And leave it at that. Be humble about this.
 

Hammick

Member
Region
USA
Nope. No explanations. You must have supernatural powers watching over you to be thankful toward. Make burnt offerings to Zeus, god of lightning? The whole battery could have discharged the entirety of its stored energy in 1/10th of a second burning everything around it in a flash chemical fire. Let's say Luck. And leave it at that. Be humble about this.
Yep Zeus had my back. We have an offgrid vacation place with a 48v solar system I installed myself. Working with those batteries (previously Trojan lead acid) and now 280ah of LifePO4 Lischen cells I am super careful. I wasn't being careful at all with this bike battery and the Lion cells are more volatile than LifePO4 from my understanding. I'm lucky I'm not blind.
 
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6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
As others have said, this could easily have gone from a fortuitous event to a disaster! I'm glad it was the former.

I'm not familiar with Rattan bikes but many brands have batteries that go into deep sleep mode after a period of disuse. My Pedego batteries go to sleep after around a month on the shelf. They need to be connected to the charger to wake up. My, guess is there was an issue with the sleep function circuit in the BMS which was cleared by the short.

It will be interesting to see if the problem repeats after the battery again goes into sleep mode. Hopefully, the new charger will work as it should.

Please keep us posted.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
As others have said, this could easily have gone from a fortuitous event to a disaster! I'm glad it was the former.

I'm not familiar with Rattan bikes but many brands have batteries that go into deep sleep mode after a period of disuse. My Pedego batteries go to sleep after around a month on the shelf. They need to be connected to the charger to wake up. My, guess is there was an issue with the sleep function circuit in the BMS which was cleared by the short.

It will be interesting to see if the problem repeats after the battery again goes into sleep mode. Hopefully, the new charger will work as it should.

Please keep us posted.
My bet too. You got REALLY lucky with a quick reset. I wouldn't try that again though....