Motor vs Battery rate of power loss

Tuner

New Member
Just signed up. As a life long offroad motorcycle racer and mountain bike rider, I just took delivery of my 2017 Haibike Xduro 8.0 Saturday - amazing! I was sound asleep regarding E bikes until about two weeks ago.....wide awake now!! Can anyone tell me the approximate rate of motor power loss as it relates to the battery level? (Bosch Performance CX)
Thanks
 

JohnT

Active Member
I'll give this a shot. Sorry, I'm not familiar with your bike's specs and didn't bother to look them up.

Power, measured in watts, is volts times amps. A fully charged battery has more volts than a depleted battery, but max amps drawn should be about constant, so power should have a linear relationship with voltage.

If you have a 48v battery, it should be something like 54v fully charged and maybe 42v depleted. Theoretically, that gives you (54-42)/54 or 22% less power from a depleted battery than a full one.

When you drop to a certain voltage, the bike will shut down to protect the battery. I think some bikes will limit available power near the end to save battery, so power might be reduced by much more than 22% at that point.

There are other factors. There's something called "voltage sag". While pulling a lot of amps, the voltage will actually drop temporarily and go back up after. The amount of sag can vary, depending on battery chemistry and quality.

I'd better stop here, before this post gets too long. Hope this helps!
 

Lost

Active Member
An ebike will go anywhere from 15 to75 watthours/ mile. There is a great page somewhere with real world results that you can find.
Find out how many watthours are in your battery and divide it out. And subtract a little for life's realities. A great many factors including terrain, temperature, the amount YOU pedal, and bike configuration will skew it one way or another. I have only been interested in them for a short while, but some will be lucky to go 10 miles, some will go 50 or more.
 

Tuner

New Member
I'll give this a shot. Sorry, I'm not familiar with your bike's specs and didn't bother to look them up.

Power, measured in watts, is volts times amps. A fully charged battery has more volts than a depleted battery, but max amps drawn should be about constant, so power should have a linear relationship with voltage.

If you have a 48v battery, it should be something like 54v fully charged and maybe 42v depleted. Theoretically, that gives you (54-42)/54 or 22% less power from a depleted battery than a full one.

When you drop to a certain voltage, the bike will shut down to protect the battery. I think some bikes will limit available power near the end to save battery, so power might be reduced by much more than 22% at that point.

There are other factors. There's something called "voltage sag". While pulling a lot of amps, the voltage will actually drop temporarily and go back up after. The amount of sag can vary, depending on battery chemistry and quality.

I'd better stop here, before this post gets too long. Hope this helps!

Thanks JohnT....... Exactly the information I was looking for. Appreciated...