I noticed that after upgrading from Loki to Juno my battery life was severally decreased. 
I have a Dell XPS 9550 with a NVIDI GeForce(R) GTX 960M. 

- I've installed `tlp` and `tlp-rdw`
- I've addded the nvidia graphics drivers ppa: `ppa:graphics-drivers/ppa`.
- I'm using nvidia-driver-...
- I've installed all the recent updates
- I've switched to `intel` using `prime-select`.

I noticed however when checking powertop Tunables, when running from battery the following item:  

    Bad           Runtime PM for PCI Device NVIDIA Corporation GM107M [GeForce GTX 960M]

I also noticed:

    The battery reports a discharge rate of 20.9 W

When I switched the NVIDIA item from bad to good I got:

    The battery reports a discharge rate of 12.4 W

Which is quite a significant drop. 

So I tried to make this setting permanent. The simplest way I could figure out how to do was:

- Create: `/usr/local/bin/powertop-tuning`
- Make that file executable
- Add a powertop SystemD service that executes that file.

Now the battery life has improved and the powertop tunables always indicates good for the Nvidia card.

I found this possible related question, but the issue seems solved and should have been back-ported to Ubuntu 18.04 already.  
https://askubuntu.com/questions/1037977/optimus-nvidia-gpu-turned-on-whatever-prime-select-says/1045767?noredirect=1#comment1799551_1045767

Questions:

- Why would the NVIDIA card still use power even though I selected Intel?
- Is there a better way to disable it?
- Is there an easier way to achieve this powertop tuning?