Battery discharge cut out voltage

[D C]

Could anyone tell me what the cut out voltage on discharge of my 36 volt 10 ah pannier rack type battery is likely to be at the point when it should cease to give power?
I have a voltmeter fitted to my bike handlebars and on my last ride covered 35 miles from fully charged at 42.2volts and at the end of the ride I had 38.2 volts dropping to over 37 volts when under load.
I'm quite happy with this range, having taken a very hilly and predominantly off road route I thought I may well have been without power before this distance. The hub motor (250w) was still pulling strongly and felt as though it had a good few miles to go though I'm guessing that the voltage may go down rather more quickly from the point I had reached.
The battery is stamped MXUS 130404 3610B DFD
the controller serial no. is KT36ZWS-XFK016B and is labelled as Input Voltage DC36V, Min Voltage DC31+/- 0.5V, Max Current 14+/-/1A.
and Speet Set 1-4.2V
I'm curious to Know what percentage of power may have been left in the battery but realise this may be a "how long is a piece of string" type of question.

Edited to add that after the first 12 miles I had 41 volts dropping by around 1 volt under load, then at 24 miles I had 39.9 volts dropping again by about 1 volt under load.

Dave.

 

[KirstinS]

I have been told by those far more knowledgable than I that by 36v you are nearly dead

 

[D C]

I have been told by those far more knowledgable than I that by 36v you are nearly dead

That works out quite well for me as at 40 miles I am usually nearly dead!
Dave.

 

[flecc]

The cut-off point on most e-bikes under load is set at about 31 to 32 volts, and your figures give yours as 31 volts +/- 0.5 volts, so it's typical. I can't say how much is left in your battery when at 37 volts under load since the characteristics vary according to the motor/controller and battery combination.

E-bike battery meters use voltage as an indication of content, but they are not very accurate indicators. However, I'd say you have a good few miles left when still at over 37 volts under load.

 

[D C]

Thanks flecc, that's comforting to know there may be a bit in hand,
Dave.

 

[Footloose]

Lithium cells have a nominal voltage of 3.6V. A 36V pack has 10 cells connected in series. Fully charged, each cell is 4.2V (42V for 10). Fully discharged they are 3.2V each. Appart from the top 20% of charge, so far as I know, the relationship between voltage and charge is quite linear which is why we have charge indicators on out bike batteries. It would not be so easy if we used lead acid cells which have a complex relationship beween voltage and charge.

 

[D C]

Just for information for anyone interested my battery cuts out at a 33.3 volts as registered on the handlebar voltmeter, easy to remember.
This was after around 40 miles though not that relevant as I was using leg power quite a lot

 

[Deleted member 4366]

Your voltmeter might be reading a it high, Can you check with another one?

 

[D C]

I think you are right though still reads 42.2 when fully charged. I don't make a habit of running the battery right down but next time, if there is a next time, I'll cross check.
At least I'll know when I'm close to cut off.