Sorry but you seem to maybe miss some points :
- a fresh install on any new SSD consumes more lot power because of spotlight indexing, caches rebuilding, etc. This is normal and this is EXPECTED. If you want to compare battery life (eg. power consumption) between two SSD you need to compare the EXACT same OS version with the EXACT same softwares and launchagents / launchdaemons
- a faster SSD doesn't at all makes a CPU run hotter, this is the opposite. A faster SSD takes less time to handle file copy so when you make a file copy, your CPU can return to idle state in much less time. If you don't believe me you can still boot on a 5400/min hdd on a USB 2.0 bus to see if you will have more battery life...
If you install a new NVMe SSD, you can make an exact clone of your previous system on AHCI, let the full spotlight indexing be made, and
only then you can compare battery life.
If you don't clone your previous system and make a clean install, you need to let the system stabilize to make comparisons.
You can also check for your "Activity monitor" in the Utility folder (be sure to show "all operations" not only yours) to check your CPU usage. It should be "inactive" at more than 95% when you do nothing. If not, check for software that use CPU by sorting by CPU usage.
Also be sure to use sintech adapters which are the only one to have the "devsleep" and other signals properly wired.
I got ~5 to 6 hours of battery life on a rMBP 2013" with the Bootrom patch applied and a SX8200.
I got nearly ~7 hours on the same computer with TurboBoost Switcher and a Mydigital SBX (my battery has 460cyles and only 83% of FCC)
PS : on a 2013 boot time on NVMe is not at all slower than with AHCI with proper sintech adapter and boot disk properly selected in the "startup" control panel.