These are 14" "Ultrabooks" with the same rated battery capacity, dimensions and almost the same components.

The AMD one has 64 GB of RAM and a very bright screen (advertised as 1000 nits). The Intel one only has 32 GB and a very dim, 6 bit screen.

They both lack a dedicated GPU.

Under Linux with the AMD one, while doing basic dicking around on the internet and light Rust dev with intellij, I get a good 5-6 hours without draining the battery fully. The screen set to the minimum or almost (it's more than enough in a bright apartment – around 50% is enough when outside if the sun doesn't shine directly on it). I haven't tried this computer under Windows while unplugged.

With the Intel one, in the same conditions as above, except setting the screen a good 2/3-3/4 (the screen is absurdly bad and dim, so I need to up the backlight) I only get around 4 hours. Under Windows, it seems similar. But under Windows, standby seems to drain less battery (not counting when it hibernates). The PC does not have the option to enable S3.

Both laptops have the "battery saver" function on, which means it only charges to about 80% of the rated capacity. "Linux" means Arch with the latest "zen" kernel and X11. Windows is up-to-date 11 22h2. I didn't bother doing any specific tuning for either OS.

One other data point is a newer model of the same PC with a 12th gen i5 part (1240p I think but really not sure). My colleague who has it complains that the fan is always on. However, he uses Windows, and even on my 11th gen I do find the fan tends to come on fairly often, while it basically never does under Linux.

Using AMD chips is also not a magic bullet if you don't implement power management properly - a 25W AMD chip and a 25W Intel chip notionally pull the same power (although there are always games).