Dear author, which gaming laptop exactly allows you to play for hours on battery? That would only be possible by severely restricting performance. What you are asking for is impossible. Well, the way to do it would be through a huge battery (1 kWh should do it :D ) but that would be heavy and you'd hit air travel restrictions. Just like with workstations, such computers need an outlet to reach full performance and they won't last without severe throttling. They often don't even have the biggest batteries despite being big and heavy. They don't bother. If you are indeed willing to lug around that much electricity, just make it yourself. I have done it before. A trivial solution, although less efficient, is to just use an off-the-shelf inverter and stock PSU.
If you take 100 Wh as a maximum capacity for laptop's battery, two hours of gaming gives you roughly 50 W cap. That's practically ultrabook territory. Three hours would cap you at 33 W. For CPU, GPU, display, everything. 150 W TGP GPU doesn't fit into it. It makes no sense to pay for super powerful hardware unless you'll be spending enough time plugged-in.
Big gaming laptops just as workstations exist exactly because they are transportable. If you have ever tried to transport a complete desktop, even a compact one, you know the difference is big. Whether it's the space it takes up in a car or the time it takes to pack it up and set it up. A completely different experience. They really are mobile in the sense of being designed for transport.