I bought a ebike and happy with it. My 30 mins ride to work every day dropped to 15 mins.

But according to law in country where I live motor stops when I exceed the speed limit which is 25km/h.

Since I am using ebike just for assistance I am pedaling as well. But most probably I am dropping below 25km/h(very often) and motor is being on again(or is it?).

I wanted to ask how this being on-off frequently(which can be my rich imagination) situation effects the life of the battery?

  • I had a homebrew electric bike, with no Battery Management System and I had to actively monitor the voltages to make sure it didn't drop below the minimum for SLA which is 10.5 volts. Your bike will have a special BMS to keep it all healthy no matter how you use it.
    – Criggie
    Commented Jan 19, 2017 at 23:23
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    I suspect this question is sitting on the HNQ list because it sounds like it's asking whether breaking the law affects battery life, rather than the much more mundane question of whether the battery is affected by cycling fast enough that the electric assist cuts out. Would anyone care to edit? Commented Jan 20, 2017 at 13:33

2 Answers 2


Actually, when you are running the motor near the top of the speed limiter, it's the happiest and most likely drawing the least current. If you had a CycleAnalyst or other amp gauge, you'd see it reduce current as it reaches the point where the controller is turning it off to reduce the speed. The motor will be cutting in and out due to the limiter, but will otherwise be just fine with this regimen as it's effectively operating on a reduced duty cycle at full speed - optimal conditions. This is quite unlike internal combustion engines which don't like to be operated at the highest end of their RPMs.

Furthermore, when you're running at full speed, air cooling to the controller, battery, and the motor is at its maximum, so they're at their happiest thermally.

The hardest thing on an electric motor, controller, and battery is starting up from a dead stop and going slowly up a hill. This is when the motor requires the most torque and thus draws the most amps - but also has the least airflow - which means everything heats up and potentially reduces their life.

As I noted in my comments, though, the best way to extend the life of your (presumably) lithium batteries is to not drain them to 0% and to also not charge them to 100% -- but for the latter, you'll need a charger with an 80% or 90% cutoff. These are sold on the after-market. With careful dis/charging practice you can extend the number of charge cycles from 300 cycles to 900 or more.

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    There are 4 leds on the battery which shows how much battery is charged. Would it be stupid to scale how long it takes to reach from 0 to 3rd led which will help me to understand %75 is charged(lets say this time is t). So than since 90 - 75 = 15 . 15/75 = %20 , than wait t/5 more and plug off. And once I scale this I will always plug off after 6t/5. Commented Jan 19, 2017 at 21:20
  • @RoboKaren could you say a little more about why charging to 100% reduces battery life?
    – compton
    Commented Jan 20, 2017 at 2:25
  • This made me think about the ISS batteries they changed a few days ago. Those are spec'd for 60000 cycles...
    – njzk2
    Commented Jan 20, 2017 at 3:27
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    There's a lot of technical discussion in endless-sphere on why lithium cells prefer to not be charged to 100% and not discharged to zero. But it's not just lithium, nickel based batteries also show the same characteristic. The comment space here isn't the best placed for such an explanation.
    – RoboKaren
    Commented Jan 20, 2017 at 4:14
  • And @KadirErdemDemir - yes, what you propose is just fine. It's a temporal variation of what is called "coulomb counting" by EV and ebike owners. You could also use a multimeter to test what voltage you arrive at after a particular amount of tme.
    – RoboKaren
    Commented Jan 20, 2017 at 4:15

Sounds like you have a Pedal Assist system, where your work is augmented by the motor at speeds under 25 km/h

Most modern systems will stop the motor assist at all speeds above the limit. If you drop under 25 but are still pedalling, then the motor will kick in and give you some assistance. That's what its there for.

If your forward speed remains under 25 then the motor will be assisting as long as you're pushing the pedals around. If you coast, the motor will stop too.

SO the battery gets a wee rest between activations. On older SLA batteries this would be the best way to get the most energy out before they're "discharged" but in modern lithium batteries it will make very little difference.

In short, don't worry about your battery - its a consumable item and will need replacing in some number of years no matter how well or poorly you treat it.

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    Agreed. The best way to stretch battery life (number of recharge cycles) is to only charge to 90% (around 4.1v) and only discharge down to 10% (around 3.5v). Not discharging to zero is easy (just don't run your battery dry), charging to only 80-90% requires a special charger with a charge limiter.
    – RoboKaren
    Commented Jan 19, 2017 at 19:52
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    I don't know if I have a Pedal Assist system will it be ok if I share a link to my bike in a comment or in question. I afraid since I am new to this community and it will be like commercial Commented Jan 19, 2017 at 19:53
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    In addition, if you're pedalling hard enough that you exceed 25km/h, then the electric assist probably isn't working at its hardest. This will prolong the life of the components (the effect on the battery specifically isn't significant, but it's in the right direction).
    – Chris H
    Commented Jan 19, 2017 at 19:54
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    By all means post a link. It's all about context and declaring any involvement: you've told us you're a customer which is perfectly suitable.
    – Chris H
    Commented Jan 19, 2017 at 20:07
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    But if the motor comes on when you pedal, as it sounds from your question, then it's pedal assist
    – Chris H
    Commented Jan 19, 2017 at 20:08

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