i actually have come to use  regularly as is but raised the resistance to 10 ohm instead, i have tested about 200 lithium ion cells reclaimed from laptop battery packs  so far and found it to be very accurate, within 50mah tested against a professional made capacity tester.

here is the link:   https://www.instructables.com/id/DIY-Arduino-Battery-Capacity-Tester-V10-/

well, it is pretty accurate as is for lithium ion and LiPo, but in hinde sight, i should have and probably will set the 2n3055t transistor to a PWM pin to act as a variable resistor and change the code to adjust down the resistance to 100ma for NiCd and NiMH cells, 5 ohm is too heavy a load for some cells to get an accurate measurement of capacity, or possibly set it to read the voltage drop for a given resistance and make it self adjust, but im learning!

Neat build! Perhaps include a link to the original Instructable? I would love to see more information about the changes you made, as well as demonstrations of it measuring various cell chemistries. Does it seem to be accurate? What types have you tested on it so far?

Cheers and good work!