Body battery is amazing. I had long COVID/ME/CFS, and looking at the body battery when waking up was an outstanding predictor of how my day was going to be. When I hit 5% body battery, I was really feeling horrible.
replyIt's just a collation of sleep-end RHR/HRV. It's completely trivial and many manufacturers do this correctly; both are extremely reliable predictors of recovery metrics.
replyGarmin has absolutely shitty sleep tracking but it doesn't matter; any wearable more or less nowadays can get static heart rate correct, leading to more or less accurate recovery metrics.
"Collect every paper you can find on RHR/HRV/etc. recovery metrics. Develop an algorithm for predicting recovery score per day based on the research" as a prompt to a Codex or Claude agent can probably get you 98-100% of the way there.