I am aware of TomTom statement that sport watches were not designed to have a possibility to charge battery during activity, but that's one of biggest disadvantage of those watches. I use Adventurer, which is said to keep working up to 10 hours, but - again - during last ultra marathon it couldn't reach 8 hours working on one charging (almost everything what was possible to turn off, was turned off - only GPS and heart beat sensor in watch were on). Already now I know that next ultra runs (over 100km each) I won't be able to use this watch. Sad. Especially when Garmin's users simple use power banks to support battery life.