Just a suggestion but you might want to look at the following.
https://www.skyrc.com/BD200

Allows you to set discharge current and cut off voltage. Displays consumed mAh over discharge period.

You do have to calculate the cut off voltage per battery type X cells in series. There are many articles (and debates) on safe dishcharge cutoff voltages for various lithium batteries chemistries on line so I am not going to make a suggestion as to cut off voltage.

I just wanted to suggest the above tool as I find it useful. I fly very large scale R.C. helicopters which use rather large battery packs at high discharge currents and I find the above very useful for analyzing my packs.
YMMV