Interesting. That hasn't been my experience of the 2 devices I've had (I dropped the first and smashed the screen)
I did an 11 hour audax a couple weeks ago in one charge
But you can reduce battery life by having Bluetooth and wireless on and using sensors, HR monitors etc
I have one, it's great. Where did you get 8 hours from? I've done 12 hour rides without a charge several times using the map and routing.