In conjunction with tlp and powertop, I use a program (in Arch Manjaro) called “auto-cpufreq” which (on battery mode) cripples your laptop’s performance in exchange for a few more hours of run time. It works well for my AMD Lenovo ThinkPad E595. Mileage may vary.
TL;DR
tlp + powertop + auto-cpufreq = 
