Battery Problems

[Martin (Mallorca Guiding)]

So, it's not even a year since my DIY self build eMTB and things were going great... but all of a sudden when I was out on a ride my battery stopped, whilst still showing 82% on the controller! I stripped it down, checked all terminals etc etc.. but then I noticed the battery itself has a button on it with a little light window to check power..>I pressed this and nothing lit up! (lights up green when it has life!) I got this bike build from Joye Bikes, which was a it that had the frame and the motor and the battery. Customized Lithium battery, Customized Lithium battery direct from Changzhou Joyebikes Co., Ltd. in CN
If u have read my build threads, u can see I did have some teething problems but everything has been fine until now!
So, I got the eMTB home (bloody hard ride home with no battery!!) and I took the battery out and stuck it in the charger. I left it for a few mins then unplugged and did the pressing of the button thing on the battery again, and it lit up solid green!!! I put it back in the bike and switched on the controller and low and behold.. It showed 83% power left!! So, I took it out on another ride and this time it stopped at the start (after 5 mins) The battery was fully charged and it showed up as 100% on the controller until it stopped! I took battery out and again , the light would't come on when I depressed the button on battery to check! I took it back and totally stripped the bike down and cleaned all connectors etc etc.. I did everything!! I plugged the battery into the charger for a min. then removed and pressed the button on the battery and it lit up green again!! Put it back into bike and again, it all lit up again and showed 100% charge. So, everything was good again for 4 rides... all running perfect, then yesterday.. 1 hour into a ride, it did it again!! Same scenario, I removed battery, and no light came on when I depressed the button on the battery to check it....but it was showing up as 60% on the controller before it stopped! I'm thinking faulty battery from these guys at Joye Bikes!! I have notified them, but I had nothing but hassles from them when I first got his kit and the Bafang motor was faulty and had to be sent to Poland to be fixed etc.. and I have no idea if they shall send me a new battery.. as they are in China... But I did pay them by Paypal.. so I do have that to fall back on, as it is not even 1 year!! Has anyone else had a problem like this? It isn't the temrinals etc etc.. can only be the battery.. as I have checked everything else, and well, It has to be faulty as the green light doesn't light up... when it should! I left a link to JoyeBikes site to show u the type of battery it is... (48v 17.5) - any info or advice would be most welcome... (update, it just happened again to me this afternoon... I was out and the battery had 69% charge left, what it said on the controller, but it just stopped - I took battery out and pressed the charge check button, asn no light... So I got home, made a video to send to supplier in Chyna!! and showed me clearly with no power, removing battery and depressing the button to check and no light, I then kept video running whilst I took it indoors, shoved it in the charger for 10 seconds, unplugged.. pressed button check and it light up green, put it back on bike and it started up again and shows 69% power left in battery... so beats me....As ever, the chinese supplier - JOYEBIKES, are dragging their heels and talking to me as if I sailed down the river on a banana boat!!!)

 

[arTNC]

Three years ago I built a 2003 Santa Cruz Bullit mid-drive with a Bafang BBSHD for mountain biking. I bought the motor and other components for the build mostly from Luna Cycle. At the time this was in the throes of covid and Luna didn't have the battery I wanted. I would have trusted LC to provide a good battery and back it up. I saw quite a few of the cheaper unknown source batteries on Amazon and other sources. Surely there were one or two good ones mixed in there, but who knew?

I think your experience is the kind of thing you can run into with these suppliers when things go wrong. I wouldn't touch them with a 10-foot pole. Hopefully you will get a response and perhaps you may get a replacement battery, but it can be a real crapshoot with outfits like this. I went with a Bicycle Motor Works battery out of Pennsylvania that uses Samsung, LG, and other name brand batteries in their packs, and they provide good documentation for such. I have used that battery for 3 years in actual mountain bike use, and I mean a lot of use for aggressive off road with a motor that likes lots of power. While trouble can strike any supplier once in awhile as far as a failure or breakage can occur, I would not be surprised if you end up having another problem with a replacement battery from this source again...but maybe not.

From a technical end, it sounds a little like a BMS (battery management system) module in the pack is failing and inconsistent. This is one of the most important elements in a battery pack to provide proper function, service, and safety.

 

[Martin (Mallorca Guiding)]

yup... thanks for your reply bud.... It is a bummer.... and what seemed like a great idea doing a self build... I wish I really hadn't and just gone with a brand name!!! hey ho... live and learn... The actual bike is brilliant... when it goes!! haha...sometimes I get a full ride on it for a few days... then like today... only till 69% and off it went..... luckily today.. I only had downhill to go!!!

 

[Bengy22]

If I had to guess one of the cell groups is way out of balance causing the bms to trip power. Unfortunately if you don't have much experience working with electronics this probably will be outside your comfort zone to fix. To confirm this you could open the battery up and check the bms balance wires to see each groups voltage, they should all be very very close to the same voltage (say 3.97v). If one is at 3.0v it would trigger the low voltage cutoff. Now fixing this is another issue, because it shouldn't have happened in the first case which can indicate an issue with your bms or that cell group has gone bad. You could try to charge that group on its own off the balance lead to match the other groups voltage, this could fix it but if the cell group is bad it likely will fall out of balance again causing this issue again.