I don't have any firsthand information, but I've heard power management has gotten a lot better for both Linux and Windows and the laptops advertise comparable

I don't have any firsthand information, but I've heard power management has gotten a lot better for both Linux and Windows and the laptops advertise comparable hours (with reviews not calling them out on it). There are a few name-brand laptops that offer explicit support for Linux distros. Those might gave you a better idea of what to expect.