Best way to go battery-lite is to turn on Airplane Mode. Otherwise, the simple and addictive 2D games like Doodle Jump, Flight Control, and Helsing's Fire are good for that.
Also avoid any games that use the accelerometer - some games use it just to orient the screen up/down... Another good general tip is to set the brightness to Auto. It seems that 2D games should use less battery, but I've found that the 3D game The Quest is very easy on the battery if you fix the orientation. (I've spent many hours playing The Quest. )
Definitely don't play Orbital or Tony Hawk's Pro Skater 2. Two of the most battery-draining games around, from my experience.
The very best game for conserving battery I have found is Phoenix Wright. Unity games should be avoided If you want to conserve battery. They seem to be particularly battery hungry.
Flight Control Bit Pilot Any Nimblebit game Helsing's Fire Trainyard The Quest Game Dev Story Any Keiffer Bros. game (Aquaduct, Orba, Abca...) Word Solitaire: Aurora Huebris Carcassonne (which I'm actually impressed. With how good it looks you'd think it'd be a drain)
First of all to make your battery last longer you need to stick to the standard iPhone battery saving rules, for example: http://forums.macrumors.com/showthread.php?t=525741 This way you can always save a couple of % of battery, and who knows, maybe because of that you will save someones life one day Next thing, you have to keep in mind what drains the most of battery when it comes to games. The biggest battery killer is obvious 3D graphics. The more advanced it is, the more energy it drains. So the conclusion is this - you want your battery to last longer, stay away from games like Aralon, Infinity Blade, Galaxy on Fire 2, Space Miner, Revolt, Rage etc. Another thing Game Center, Openfeint, Plus+ and all the other networks. If you play a game using one of these, your battery life will be shortened. The reason for this is that the game connects many times (or stays connected all the time) when you play. If you are using 3G the battery usage gets bigger. So if it's not a problem, go into airplane mode while playing to save some battery energy. You want to play longer without charging your battery, stick to the games that have 2D graphics (good example is puzzle genre): Cut the Rope Doodle Jump Fragger Angry Birds Azkend Heroes of Kalevala Trainyard Blocks Mania Fantastic Contraption Super 7 Ragdoll Blaster Sparkle Smiles Drop/Zen Time Geeks Geared 1 / 2 Super Stick Golf From my experience most of retro pixel art games dont drain battery too fast so: Zenonia 1 / 2 Seed 1 / 2 Inotia 2 Game Dev Story (very battery lite, I can play for hours without recharging) Stone Wars Mecho Wars Rogue Runner Knights of the Phantom Castle Trace Palm Heroes Itarus all of the games from Donut Games Cat Physics, Rat on a Scooter, Castle Smasher, Jungle Crash Land, Gold Miner Joe, Sunday Lawn. Heres my hint if you want to check the battery usage of a game, play it for around 10-15mins and check the back of your iPhone/iPod. If it is very warm it means your hardware (processor etc.) is very busy, so it drains your battery like paying taxes drains your wallet : ) All of this is based on experience with my iPhone 3Gs, iOS 4.2, with a battery that is around 11 months old. I know how to take care of battery so even now I feel it is in rather good shape. Hope it all helps.