You might wanna get ipod shuffle, its light and small very portable and battery life is 8hrs and more. I really don't like those bulky music players because my pocket is already crowded with the cellphone I carry.
Small music player is better.
Get a little sansa mp3 player, in my experience they last as long as ipods do. Also you can expand them with a micro sd card. They have a simple screen/OS to help reliability and battery life, you could go for one that plugs directly into USB for conveniant charging and I'm sure they are such low voltage you could probably devise a little solar power thing to charge them from. The one thing that is annoying is that there's no charging and playing at the same time, but this is the same for ipods. The best thing about them is YOU DON'T NEED ITUNES it's just a drag n' drop procedure onto a drive.
I have a tiny clip on sansa like an ipod shuffle, I use it as a backup music source when my radio servers audio is being used. At full volume (you would never need) it last a good 8 hours.
DON'T BUY AN IPOD CLONE FOR THE LOVE OF GOD
Maybe reconsider your options
If you have a huge library of music that you regularly listen to -> buy the player with higher memory.
If you regularly listen to your music away from a power source -> buy the player with the longer battery life.
If you want an inevitably atrocious paperweight that only exists because careless buyers are tricked into thinking it's the real brand -> buy the 'clone'.