Fiido D2S no longer starts

Joined
Jul 22, 2020
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I bought a Fiido D2S back at the beginning of June. I got about a month of good riding out of it before I started having issues. It started with the power completely cutting off in the middle of a short ride. Then last week I was only able to make it to the next street over before it cut off. Now when I turn it on, I get a faint blink from the battery meter LEDs and it doesn't turn on at all.

I haven't had this bike very long so I'm puzzled as to why this is happening. Obviously this could be either the battery or the controller. The battery should have a decent charge to it as I charge it after every use. When I put a multimeter on the battery I got 39 volts (this is a 36 volt battery). I'm not too sure how to proceed. The seller says I can ship it back but I no longer have the box. I asked them if they can ship a controller and battery and see what works, but I've yet to hear back. They keep recommending taking it into a repair shop, but none of the shops near me work on ebikes and the closest one to me is no longer in business.

I'd like to tackle this myself so I can keep riding. Has anyone experience with this issue and model?
 
The battery probably has a cell group that is too low for the BMS to allow discharge. It may even be too low for it to allow charging. 42v is full for a 36v battery, so at 39v "full charge" at least one group would have to be very low or completely dead, if it is not all or most of the groups that are not fully charged.

If you leave the charger on the battery at least a whole day, while watching it (preferably with a voltmeter so you can see the voltage changes), then if it improves (has a higher and higher voltage each time the charger stops), then it may be a correctable balance issue, though it might take anything from days to weeks for the BMS to do so, if it's really bad.

If it does not improve, then there could be cells in a group that are self-discharging, internally shorted, etc, so that they cannot charge correctly (only converting all the charging current to heat instead), and then you'd need to replace the battery pack under warranty, if they will do so.

If it improves but then after charger is disconnected gets slowly worse, without using it, it probably means the BMS itself has a balancer stuck on that is constantly draining a cell group. Again, the battery pack would need replacing under warranty to fix this.

If they won't warranty it then you can repair either probelm yourself, but there is some learning to do before you start, and having the manufacturer deal with it is much easier.
 
Better late than never for an update. The seller sent me a battery under warranty last August. Everything worked well until about a month ago. After about an 8 mile ride, the battery just crapped out when I was 2 miles from home. I unplugged it and charged it which partially resolved the issue with the original battery. Nothing. A multimeter said it was putting out 29 volts. The bike was still under warranty, so instead of going through the seller, I went to the manufacturer (Fiido). I had to jump through all kinds of hoops to prove the battery was dead, including making a couple videos of me hooking up the multimeter and charging the battery. They agreed to send me a new battery under warranty, which still hasn't arrived because presumably it's on the slow boat from China. I'd be a fool to keep riding the bike after being on the 3rd battery in one year, so once the battery arrives and I can see that it works, I'm putting it up for sale. It was a nice foray into the world of electric bikes, but I can't take another chance on that happening again. I may get something a little nicer this time.
 
if the bike works fine but the battery sucks, just buy or build a better battery. batteries suck on many prebuilt ebikes, and also separately bought batteries often suck, the cheaper the suckier typically.

a good battery is probably worth two or three times as much as the bike it's on.
 
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