You could bump up to an iPod mini v2 and optionally swap out the internals for some extra storage space. The stock battery with the latest apple firmware lasts

You could bump up to an iPod mini v2 and optionally swap out the internals for some extra storage space. The stock battery with the latest apple firmware lasts about 18 hours with 450mAh. There are better 1300mAh+ batteries that offer a lot longer time though. Like others have mentioned Rockbox firmware is also available and will increase the battery life too. The iFixit site has nice repair articles for how to change the internals. An upgraded SDXC memory card with 128GB of space runs about $30. You could also buy a modded mini with this kind of storage off ebay for around $125 but it probably won't have the nicer battery life. If you really like the nano you could also swap out the nano battery to bring it back to life. It doesn't look like the storage is replaceable though.