It draws like 3 times as much power as the Switch. You're not getting 4 hours in anything but the simplest games and you're just gonna have to accept that. It would simply make the device too bulky and heavy. Realistically, you'd be lucky to get 3 hours, and more likely 2-2.5 hours. They can't go lower than 2 hours, that's the bare minimum anybody would accept, and you'd hope they'd go higher than the bare minimum, but every additional half hour of battery life makes the device bulkier and heavier, and they won't want to cross a certain threshold, since it's a handheld, making it too heavy would make it tiring just to hold it during play.
PC x86/x64 architecture is not very power efficient. It's not really a good choice for a handheld, but if you want to play PC games, it's what you need to use, so there's not much choice. It's why Apple moved away from x64, and went all in on ARM, it's much more efficient. Maybe Windows will go all in on ARM some day too, if they include x86/x64 instructions like the Apple M1 so that it can still run x86/x64 applications natively on the CPU, rather than the x86/x64 emulation Windows on ARM has now, you'd still be able to run older applications that haven't been compiled for ARM at good speed so you wouldn't be missing out on anything. But you'd only get the efficiency advantage when running native ARM applications. And you'd be making the CPU more complex since it has to run two entirely different architectures/instruction sets, increasing cost. And they'd have to keep the x86/x64 compatibility in for the foreseeable future, until emulation became fast enough that it was no longer needed, as people need to be able to run older applications. Since Windows isn't a locked ecosystem and people use all sorts of weird applications from all sorts of places, it's likely many of them would never get updated with a native ARM version.
