Your best bet for raw audio playback time would be to wait for the flash-based MobiBlu DAH-1900, which will be hitting the states soon. It has a rated battery life of 150 hours--unheard of, especially for a rechargeable player. In general, many of iRiver's and Sony's flash players, such as the T10 and the NW-E400 series, respectively, have more than 40 hours of battery life, while Cowon's iAudio X5L is one of the longer-lasting hard drive players we've used, at 27 hours on a single charge. But the best thing to do if you'll be out in the middle of nowhere is to get a player with removable batteries, such as the iRiver T10 for alkalines or an old Sony NW-HD5 (27 hours) with a spare cell, then bring along a bunch of batteries. If you like iPods, you could get a snap-on backup battery accessory. And finally, you could get a solar-powered MP3 player. Whatever MP3 player you choose, make sure you know the truth about battery life before you buy.