Unless iPod seriously upgraded their batteries in the current model, I would personally avoid it. The older version, the battery would not last long enough to download a full 4GB card (and it would take forever as well) so it is definitely not ideal unless you are on a liveaboard or do land base diving and have enough memory cards to last until you get back to shore. I bought an older 40GB iPod a couple of years ago for exactly this purpose but found that it is not very usable. The optional AA batteries pack helps a bit but still annoying.