Since the power draw is so low, I wanted to check feasibility to power it with a small solar cell.

Went to the local thrift shop and bought two solar calculators on sale for 50c and gutted them for the solar cells. Then de-soldered the solar cells and made my own solar power module, and took it out for a spin.

It worked! Unlimited power! Well well... even shading one of the solar cells still kept the watch ticking. Awesome. FYI one cell delivers 3.3V @ 2.5mA, so at 100uA burst and 10uA average running the BLE watch on solar power is whole-sale feasible.

That's very encouraging, as I was considering a re-chargeable battery with a solar element, which would bump the life to infinity.

One step at a time.

Cheers!