There was definitely a period of (at least subjective) declining battery life in the 2010s but IMO things are shifting the other way. Some devices these days have much improved battery life over what came before, like Apple silicon, the Steam Deck, and most flagship phones. They're not always an order of magnitude better than the past, but better enough to unluck many use cases (doing a long work session away from a charger, being able to game for several hours anywhere, and not worrying about having to charge my phone until I get home, respectively).
If I had to describe it loosely, we've had 3 "eras" of battery-powered computing:
- Relatively simple devices (like the Gameboy) that lasted forever, because they just didn't do much
- Full-featured personal computing finally becoming "viable" on mobile devices, but with a clear cost (I remember <1 hour battery life laptops)
- More power-efficient HW and kinda-sorta-maybe-starting-to-be optimized SW that makes full-fat mobile computing much more bearable
They really can't game for several hours though. I have an m series. If you actually are hitting the cpu the battery life is basically the same as a laptop from 10 years ago in that situation where you are bound to your charger or its dead in 2 hours. The efficiencies of this stack come from it being able to throw things onto the e cores. Most (all?) games are not written in a way to benefit from that paradigm, they might still be hammering a single cpu.
Gaming is a special case imo, and more affected by the additional power drawn for the GPU.
For CPU bound apps, there's still a night and day difference between new apple silicon vs the previous generation of x64 processors.
I've used a laptop to DJ shows for several years, always requiring AC power for anything longer than an hour. With my m1 macbook, I've DJ'd 6+ hours with no power adapter, also powering hardware over USB. It's literally a 4x improvement over my previous i5 setup.
Most of the games I play are CPU heavy incidentally, eu4 etc. I will say the biggest difference is the computer does not get very hot and the fans only spool up to 2500 rpm or so (out of their max of 6000rpm), but eu4 on full tilt will still drain the battery like it has a leak in about 2 hours or so. It isn't a very intensive game but it is one that has a speed setting where the max setting is basically "as fast as the cpu can compute." It does run noticeably faster at the max speed setting on this cpu (single core game, as expected going from 2.5ghz to 4.05ghz per core) but I don't think the battery life differences are significant. Especially considering the health of this battery compared to my 2012 intel computer (which I eventually replaced the battery for).
Outside of that the computer is good for probably 6 or 8 hours of my usual use case (ssh to remote server, a couple browser tabs, mac mail client open). I think the screen is a big power suck and I tend to find that autobrightness is putting it on max brightness setting even in an indoor room (like right now in fact). When I replaced the battery on the intel mac I was good for about 5 hours but I had to put the screen brightness on a minimal setting.
If I had to describe it loosely, we've had 3 "eras" of battery-powered computing: