There are 4 factors I suspect to be the reason of my battery improvement:
1 : disable wake on wrist movement
2: do not use your device to lock and unlock your Phone
3: I now only sync favorite contacts to the watch
4: I suspect the battery is better after a few times charging and discharging
Today I unplugged the charger at 8.35 am and around 12h30 i still had 95% left, after walking the dog for half an hour while testing endomondo and runtastic app and playing around some more I ended up with 79% at 15h40, at 16h40, still 79%.
By the way, runtastic uses less power than endomondo, but endomondo supports the heartbeat sensor. Also compared the live heartbeat in endomondo to my girlfriends polar watch (with heart sensor around the chest), and the heartbeat was pretty much the same!
Edit: 18h30 :76%
Edit2: Close your Gear manager when not using it.
8h30 100% 16h 93%