Dell precision 7750 Battery life

Part of it may have to do with how your machine is configured.  Also, this is a big clunky laptop that is focused on performance and cooling capabilities.  If you wanted something that will last 10 hours on a single charge, this is not the machine for you.  Honestly 2-3 hours real world usage is pretty darn good for a large laptop that's meant to be a desk jockey.

All of the CPU options are 45w versions
17" screens are power hogs
The dell product page does not mention battery life.
There is a higher capacity battery that you can configure the computer with. (6 Cell 97w if I remember correctly)

This machine is designed to last on the battery long enough to get from one power outlet to another power outlet.  Unfortunately the reality is that you are stuck choosing one or the other.... Battery life or Performance.

(BTW/ Most third party battery life tests are done at minimum brightness, sound off, wifi off, and BT off.  So they are not based on any kind of real world usability numbers.)

If you're just doing light browsing and want the 7-8 hours people have advertised, use the integrated graphics, as most of the power drainage comes from the GPU. When you're doing graphic-heavy tasks switchback.

I get that but my 7750 replaces a 7720 which has, probably 2-3 times the battery life - either the batter is much smaller or there is a lot of extra load

yeah - 8 performance cores ... on a battery  ???   good luck with that   .....