I decided to test out my Bryton's battery life to see how long it lasts. Normally I would fully recharge it on a weekly basis.
The Bryton 310 lasted for 7 weeks, with more than 32 hours of recording with heartrate and cadence sensors, before I decided to recharge. There was still one bar left.
So the specs in the Bryton manual of 36 hours with clear sky is probably pretty close to the mark.
OB