Originally Posted by jeffsf
My main hesitation about using a 2.5" drive is its size. By the time you add in batteries, you've got a reasonably large brick.
And other high end players (Hifiman, DX100, C4 etc.) are tiny? :D
Batteries can be made nice and flat these days... My laptop is 12.9mm thick with the lid closed... in those 12.9mm there's a aluminium casing, screen, keyboard. mainboard, coolingsystem and the battery...This battery has enough power to keep the Core i5 based laptop running for 7h under medium load.
I think a device with an outer casing a little over the width/length of a 2.5" drive, can be kept under 20mm thickness, even when using a 2 layer Lithium cell to improve battery life.
Yes that might be slightly brick-ish, but IMHO it is still quite pocketable, and think about it, you can put in a 1TB drive for less than $90, or spend a little more and go SSD...
And then there's the huge number of *enter flavour of flash memory here* to SATA converters, allowing you to use pretty much any memorycard you have laying around in a device like this.