I just wanted to make a remark about the scope of this project: I'm trying to keep it quite simple for a number of reasons.
One reason is that I'd like other people to be able to make it - I've used and benefited from a lot of open source hardware and software in the past, and I'd like to try in earnest to give back to the communities that share their work. Making a project with a small component count and a really simple premise seems like the best way to make a project "buildable" for lots of people.
I'm also not a professional electrical engineer (electronics are a part of my job, but I"m more of an informed faker), so lots of parts of this project were very new to me, including the SMD soldering, i2c implementation, and board fabrication. Avoiding things like a power-management IC that would allow for LiPo charging made this project way more approachable than a fully-engineered kickstarter-ready product.
So anyways, if you were wondering about a menu function, or an on/off switch, or a battery-recharging circuit, or a threshold/alarm mode, the answer is that those are great ideas not implemented here - but you should try them yourself!