Excellent jackbauer! The culprit for the pack voltage error is the HCNR201. The gain transfer error between photodiodes is +/-5%. To be honest I missed this parameter when designing the board and had actually used the HCNR200 which has gain error of +/-15%! Artwork was already on order so I spec'ed in the HCNR201 and implemented the software trim. This is actually an offset correction, but since the working range of a charged to depleted battery pack is narrow relative to its absolute value, I thought it would be good enough.
A trim for gain is better and changing R9 to a 10K pot as you mentioned would do that. Alternately you could change R4 to a 100K pot. If the pack voltage reports low, it could then be a 50K pot.
You probably figured it out by now, but the mod for displaying temp in C but still report as miles is as follows:
In the "line 1" section of the display routine you only need to comment out
btfss Sys_Config, 3.
It will then skip over the part to replace MTE with KTE.
Glad you find this useful
