I've found that even though some games on GOG, like BG2, are "old", they still drain my laptop's battery at a considerable rate. Other ones, like "king of dragon pass", don't. Do you know if there's a list of [good] games that won't drain battery life? Discuss!

My guess would be anything that doesn't have any actual "graphics", like KoDP, Zork and Long Live the Queen will probably consume very little .

That depends on the CPU/GPU stress the games generate. So basically all games that ran perfectly fine on ancient hardware and neither need emulation nor have quirks which stress newer systems more than old ones should keep the battery alive for a while. Reducing the resolution can have a notable impact too. The question is also what kind of hardware you have and which OS you run.

Off the top of my head I'd say Heroes of Might and Magic 2/3 but there's no guarantees, haven't checked whether they generate as little stress on Vista/7 as they did on Windows 98. You have to take the cost of the emulation into account, though. A native Windows game with 3D graphics may cause less stress than an emulated text adventure like Zork.

Oh right, forgot about that...

In that case, maybe Eador: Genesis could be what the OP's looking for ?

Any game not involving electronics? Yahtzee, Twister, Soccer, Poker, Pool, Dungeons & Dragons...

Joke aside, F4LL0UT is correct (Heroes of Might and Magic 2 is likely tough though, since it runs in DOSBox). Though you might want to check if the 3D acceleration is enabled in Baldur's Gate 2 and flip that switch to see if that changes anything.

Turn based games should do quite well in this regard.

As above.

Please note that laptops aren't intended for gaming, at least not as a primary purpose under most suppliers. The batteries are expensive, and even those computers with the best life are intended for web, writing and as a mobile work space, all with applications that pull little cost to the computer resources.

Games with less draw in this case are going to be ones that aren't very modernized. It takes more effort to design a 3D world and animate it at the same time than something at 2-D. The same way, the smaller the game world at a time, the less resources. In this aspect, Beyond Good and Evil costs more to use than Reus, which has more draw than FTL, which has more draw than Spacechem, which has more draw than ultra-minimalism Zork which has no graphics.

But, this isn't the full equation. Computers are designed somewhat to optimize settings. The same thing happens with games, and they will switch around resources to run at a decent speed. Because of this, you risk having a situation where totally different games with totally different requirements, are optimized to a point where they draw the resources regardless. This isn't going to happen say for something like Zork, and a game like Beyond Good and Evil because they are so different, but for something like Reus and FTL, you could potentially run into this situation.

What to do? First off, if you're gaming, keep the battery charged, and connected to a nearby outlet. Look for games that have smaller install/download sizes as those will have smaller resources a majority of the time. Lean towards 2-D over 3-D games, reduce settings as is reasonable to your experience, and turn down the volume. Listen through a pair of headphones or earbuds if you struggle to hear the game. If possible, reduce the screen brightness, as this will also have a heavy effect on your battery time. These should all help to give you the longest possible time on your computer to game.

TC said BG2 drains batterly life a lot, and I doubt that's because of complicated graphics. Perhaps there's no vsync so the GPU is draining the battery by running the game at 3000fps?

And don't forget you can play with power options to draw less power at the cost of performance. I wouldn't bet on it - CPU will be doing a lot of processing in that game. I know it's one of the games that would overheat my laptop (which I never bothered to dust out so even Hulu would overheat it) unless I reduced my max CPU processor speed using advanced power option settings.

If framerates don't bother you, likely any turn-based, animation movement-lacking game, you can use tools to force a lower framerate along with playing at a lower eye candy, should help a lot with battery life.

If your laptop is fit for a SSD and you have some spare cash consider purchasing one if you don't own one. Their power consumption is much lower than a mechanical harddrive.

The reason why Bioware/Black Isle Studios RPGs (like Baldur's Gate 1-2, Icewind Dale 1-2 and Planescape: Torment) drain your battery fast is this:

http://www.gog.com/forum/baldurs_gate_series/100_cpu_usage_modern_computer_whats_up

That is, for some odd reason they try to use every CPU cycle they can find (on one core), no matter how powerful your CPU is (on newer i7 CPUs this is reported as 50%, but it is still the max the game can find). The CPU usage stays high (max) all the time, also in menus etc.

Oddly, according to reports the new EE version of BG also has this same "feature". But I haven't tried it myself.

The workaround that I sometimes use (e.g. now that I play Icewind Dale) is to set the the maximum CPU speed on my laptop's power manager settings to lowest. That way the laptop will throttle how many CPU cycles are given to the game (or for the PC overall). The games still run the same as with CPU setting on highest, maybe the loading times (from HDD) are somewhat slower. After all my laptop's HW specs are way over the requirements of those old RPGs, even with CPU throttling.

In my case I don't care about battery life, as I play the games power plugged in, but throttling the CPU manually still helps running my laptop cooler (without fans spinning at max speed all the time) when I set the CPU power settings down when playing those misbehaving old Bioware RPGs. Many newer and more advanced games (like Diablo 2, Wheel of Time etc.) use less CPU than those Bioware RPGs.

There are apparently some other older games too which like to use the full power of your PC for nothing. E.g. Arcanum was mentioned in that linked discussion, I haven't tried it myself.

I can imagine that it's for similar reasons as with Tiberian Sun and Red Alert 2. At least those two have some hardware accelerated rendering method which massively slows things down on more modern systems. Up to Windows XP you could solve such issues by temporarily deactivating hardware acceleration via dxdiag, sadly it's not that simple anymore since Vista.

Edit: Woops, I somehow managed to skip everything else about your post except for that "BioWare RPGs run worse than newer games" part. Sorry, I'm tired.