[tyhoff]

It’s primarily about the number of hours. At Pebble, we’d be able to get a pretty good gauge on battery life with about 10-20 devices and about 24 hours worth of data. We recorded the battery’s percentage drop over the course of each hour, averaged all samples together, and then used that to estimate how long the battery charge would last.

This strategy is covered here: https://interrupt.memfault.com/blog/device-heartbeat-metrics...

Of course it’s better with thousands of devices, but we were always surprised how accurate it was (as long as we had a few Android users in the office - it reliably got worse battery life due to worse Bluetooth performance)