How does battery voltage relate to capacity remaining?

[DavePat]

After my last ride on the Woosh Sirocco CD with the 15AH Battery I had covered 26 miles. I checked the battery voltage and it was 36.4 V, I then fully charged it and it was 42.2 V.
The LCD indicator on the bike and the lights on the battery never seem to be consistent indicators of how much battery I have used.
I have never yet flattened the battery but the longest trip so far was only about 36 miles. Any way to use the voltage drop as an indicator of what's left, I guess it is not a linear relationship?
I tried to google the info without success or anything I could understand anyway.
I know someone has the answer.

Dave

 

[flecc]

The answer is mainly that the voltage drop is not linear as you've guessed. I've found sometimes quite large disparities in the mileage obtainable for each step on typical battery 5 LED indicators, though varying terrain can make it difficult to be sure how much is due to that factor.

It would need a test in completely flat country on a windless day to get a better measure of accuracy, luxuries I never enjoy.
.

 

[BAH48]

My Bosch control system seems to be reasonably accurate, the algorithm must be quite sophisticated to predict the remaining mileage which is pretty much spot on.

 

[trex]

the battery's charge versus voltage is fairly linear between 32V and 40V.
At 36.4V, I reckon it's about 35%-40% remaining,
The useable remaining charge is a bit less if you ride fast.
This is the typical discharge curve, for e-bikes, the discharge corresponds to the graphite electrode's plot. Your battery is 10S5P - follow the horizontal line from 3.64V on the vertical axis.

 

[DavePat]

Thanks trex, when I get my repairs done after bank holiday Mondays tumble I might start to collect some data on my rides and see if it makes any sense over time.
I tend to have 2 favoured routes and I appreciate a number of factors all play a part in discharge.