I've been conducting an experiment over the past couple of weeks looking at the effect of different backlight settings on battery life.
No backlight. 2 hours riding. 100% down to 92%
20% backlight (my usual setting). 2 hours riding. 100% down to 88%.
100% backlight. 2 hours riding. 100% down to 61%.
Conclusion: Each 10% backlight consumes an additional 1-1.5% battery life per hour, although I haven't run intermediate settings to verify. 100% backlight is a huge power drain.
(Note: the above figures were with a chest strap, so no OHR. No timeout on the backlight. GPS only - no GLONASS).
