Battery or.. controller problem?


New Member
I just bought an electric bike a week ago, a cheap one from the Vivi brand from Amazon because I only need it until work and back. The controller on the buttons is not digital and has 5 lines when the battery is fully charged. Yesterday while I was coming from work the battery suddenly dropped from 5 lines to 1 line,the controller did not turn off, nor the battery but with throttle at max the battery it was delivering power in short short power brakes, on the pedal assist does the same thing,again the controller it doesn't stop it just shows me a line or two sometimes as if the battery isn't charged, the indicator on the battery when I press to see how much power the battery has, it lights up once quickly and then shuts down.I'm a newbie with this things so I just wanna know if it's the battery problem or the controller or idk..thanks for you patience. I will post some photos with bike and controller


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K PierreR

Well-Known Member
The problem is likely the battery capacity and the bike is operating normally.
Batteries work by chemical reaction. As the reaction takes place the atoms for the reaction have a harder time finding other atoms to react with because of the newly formed molecules that are in the way. As that happens the voltage drops in the battery. If the battery is large enough for the task then the chemical reaction can keep up. If lithium ion batteries are discharged too far they are junk. To protect that from happening the battery has a BMS (Battery Management System). When the voltage drops to a certain level the BMS cuts off the battery to protect it. If the battery still has charge but is voltage depressed (battery sag) the voltage will recover and the BMS will turn the power back on. What you experience is intermittent power spikes.
You have two choices. Get a bigger battery or slow your ride down so the battery does not experience severe sag. You are likely pulling to much power from the battery with your riding style. Severe SAG is very hard on a lithium ion battery.