Other battery types, like laptop batteries (uses I2C) are not supported.

This info should really be in the top-level README

I think the home page is LLM-aided, the design looks very familiar and wording like

[...] no software to install, nothing to set up. Plug in an Arduino, flash the firmware [...]

gives me pause. I am an actual embedded software engineer, and I would not classify finding, wiring (with resistors!) and flashing a microcontroller board as "nothing to set up".

fed all this to the robot to find that it's targeted at Makita battery packs. the word "makita" never once appears in the front page and it seems like a pretty important detail.

I couldn't find it on a short inspection.

Insert a battery and press Read battery

Where do you insert the battery?