I have had success with my Late 2011 MBP 15 which had suffered from the failing discrete GPU issue.
Firstly, I ran a security update which failed and left the machine unable to boot. I think this was because the AMDRadeon3000 kext file was missing from the library folder, - the first “fix” I had been using to get her running again a couple of years ago. This left everything working, sleep, brightness etc. but the machine did still get hot and run the battery down fast.
So, I had to rebuild a High Sierra boot volume on a USB drive attached to my 2015 MBP 13 (which luckily will boot into HS, and hence allow me to make the USB boot drive.
I then used the HS USB to Boot the 2011 MBP 15, and with the aid of the well documented procedures on the web, I removed the GPU kext again, but this time I also disabled use of the GPU by booting into single user mode and and entering a magical command that has lots of zeros, ones and percentage key characters which sets the integrated Intel Graphics to be used instead in the NVRAM.
Another command line instruction loads the kext after booting the machine, which apparently is the key to ensuring the discrete GPU doesn’t idle and drain power. - This is set up as a LoginHook to run automatically on startup.
Then obviously, I used CCC to clone the USB to the MBP’s internal drive system / boot partition.
I have set up a script in the root directory so if I need to reset the NVRAM, I can easily power the GPU down from single user mode with a couple of keystrokes, restating the custom configuration.
And also, should another security update come along, then I will just put the AMDRadeon3000 kext back before running the update. - I also now keep a full CCC backup of the boot drive as well.
Now the machine really just sips power. The ageing 993 cycle battery reports 76% health, but she runs for ages and obviously also just doesn’t get really hot anymore, so the fans spin low. I use Macs Fan Control too and even with conservative settings they still rarely run above 2500rpm.
The machine has an SSD in the SATA 3 drive bay and a 1TB HD in the optical bay using an OWC data doubler adaptor. There is still useful life for a 2.2GHz quad core i7 MBP !
This thread is also relevant → Ageing MacBook Pro issues