I could say over design, but zealous sounds more purposeful.
So, zealously over designed peculiar digital life-game controller here. Added a coin cell holder for a 3v coin cell (12mm) to keep the RTC clock going if power drops or is removed. Added an on-off switch(!) Added two extra components to the power management circuit — a MAX4651 for the really off situation in which I use a removable battery and insert the battery backwards, and a MAX6439 battery watcher deal that’ll signal the MCU if the battery goes below a specified (factory trimmed) voltage, pull down reset if it goes super low, and signal if it rises back above a threshold, with a bit of hysterisis. Problem was that the thing could drain the battery into oblivion which made recharge long and tricky. But, frankly — now with the on/off switch and battery back-up for the RTC, it’ll be much easier to charge over USB. I hope. Found some small LiPo batteries from an iPod Shuffle battery replacement kits, of all things. One is 230mAh, the other one says it’s 400mAh but it’s marked 330mAh. Close enough for Jazz. It’s about 37mmx22mm.
Also I found this operation:
They sell small, flat, light LiPos with decent capacity (160mAh+/-), but much more expensive and harder to get.
Curious about what’s what? The Flickr page has “notes”.
Update. The iPod replacement batteries work great so far.