We have seen some limited battery issues with the 770s built in internal battery and power issues in general when correct steps are not taken to power the 770 correctly.
Overall, the biggest difference between the two cameras is that the VDB750 does not have an internal battery. While the camera will not work without power, the camera has less power related issues when compared to the 770 and older Alarm.com Skybell cameras.
More information on both including specs and features can be found below: