Looking at the specs, the RT is slated to have a 31.5 WattHour battery and the Pro is slated for a 42 WattHour battery.
A 42 Watt Hour battery plus an ARM processor in the "New iPad" yields about 10 hours of WiFi surfing on the net.
I would expect to see advertised battery life between 6-9 hours for each tablet. The Pro should have a real CPU (core i5) and will take a bit more power, but it does have a bigger battery.
In my experience, the biggest drain on battery are:
- Screen Brightness
- WiFi
- Bluetooth
- GPS
If I have my current tablet at max brightness, GPS on, WiFi on (doing turn by turn directions) I will get about 5 hours from my tablet.
If I have all radios off, minimum brightness, reading a Kindle Book or watching 720p video, I average about 10 hours for the tablet battery (which it advertises about 9 hours).