Brand new Dell 7000 series Inspiron 15 runs perfectly under Mate 18.04, but battery life has crashed from up to 8 hours on Windows 10 to barely 1.5 hours. TLP installed, but doesn’t seem to have made much difference. This seems to be a common problem, and must be one of the last remaining reasons stopping people switching from Microsoft, so is there likely to be a real solution any time soon?
Hallo Philip
Have you seen this?
It might give you a few ideas. 
Edit (added) 30.12.2018
You may also find this to be of interest:
https://www.phoronix.com/scan.php?page=article&item=laptop-battery-july18&num=1