Well, i don't see anyone else pointing to a 'mass storage' solution (and yes, CD-ROM goes qualify as 'mass storage') that can do 100+ hours on it's standard charge without extra powerpacks connected.
The D-NE1 did it's 130hrs max rating (which is internal cells only rating), and that was with mp3 playback (the official rating is based on 48K ATRAC3PLUS, which is less power impact intensive) - given sufficiently high cap ni-mh's, even the iMP's could (using favourable conditions) go close to that kinda distance (about 3/4 would be more sane expectation).
I was probably dead lucky to get that OTT performance out of my deck, then again.. i somehow seem to pick the ones that do go the distance and exceed the specs in many cases, but you'd need a pretty heavy duty ext pack to get a HDD unit to go a proportionally high distance endurance without relying on total use of high-cap rechargable packs.
As for 'CDs' taking up lots of space, far from it - if you know how to pack yer bags well when travelling, it simply aint a problem (you can easily carry them in card sleeves, to protect them and seriously reduce the risk of damage).
And the loss of a CD-ROM and it's content due to an accident - well, that's no different to an accident with an HDD - if it takes sufficient a blow to ferk up readbility of the HDD's contents, you gotta rework the content (oops, now where's that ferking computer i need... !!!!, when i'm in the back of nowhere) to get it back into working order again and hopefully you aint screwed up the content...
So ask far as risks go, a 20p blank CD and a short internet cafe session (lots do allow you to burn CD's in their facilities these days) to remake a 700mb content - vs whatever aggro to get the HDD and contents back into A1 operation again (you'd be on an internet connection a good while, expensive at internet cafe prices, to restore the better part or the whole of a large DAP HDD's contents from an online accessible backup).
I know which i'd pick still
