I'm not much of a developer :), but anyway I like the #precursor project a lot.
I'm not sure whether a custom battery will be an improvement in every aspect, but the goal for the project is not reached, yet, anyway.
If you are able to use such a development platform - I'm really looking forward that it becomes an alpha testing platform to try :).
https://www.crowdsupply.com/sutajio-kosagi/precursor/updates/stretch-goal-larger-battery
Yes, that's true. As I understood it aims at something completely different: you can build (test/use) sophisticated password stores, 2FA devices, wallets for crypto currencies or whatever else needs a hardware basis completely trustworthy.
It gonna be the open hardware device running open source software that protects your digital life - whichever functions will be implemented.
I'm really looking forward to read about the first ideas and projects and follow them!