So did some tests today.
I put it to 17 amps, rode half a mile, then changed it back. Literally couldn't tell a difference at all, so figured better put it back stock. Maybe if you derestricted it and went around on assist 5 all the time you might be able to tell. I might try it down 2, to 13Ah to see if that changes anything as far as range goes. What does it even mean, if the battery is 13Ah shouldnt the controller be set to 13 too and not 15? Is the current setting on the LCD just the max current given to the battery?
Anyway battery tests.
Basically I got 52 miles (about 5 of which i did yesterday, so im very sore right now having done 47ish miles today), 52 miles before it wouldn't assist me at all. LCD still showed 1 bar though and didn't flash empty which is odd, maybe it doesn't have that feature will have to check the manual.
For the last 8 or so miles, it would maintain 13-15mph on throttle alone as you can see in this video, where i use throttle alone and assist as well:
Steep inclines it really struggled and took some effort on my part, as this video shows:
So thats basically how it performed for those last 8 miles before finally dying and not helping at all.
I'm going to measure the volts after it has sat for about an hour, then charge and time it again. So I guess this is the best I will get from it, still not as good as it was, but its not too much different. If changing the assistance powers won't void warranty, I might experiment with a 'between assist 1 and 2' power level and see how that affects range.
Edit: 34.1V, putting on charge now