Perhaps we can have a more constructive conversation if we more clearly define what we mean by 'portable'.
If by portable you mean you can use the CD player while physically moving with it, then the D-25s is not the player you want. As stated, it has no-anti skip protection and would have a hard time playing continuously on the go while in your hand while walking or jogging or in a car.
If by portable you mean small enough to fit into a bag and use in a battery powered situation, like on an airplane, at your desk at work or while studying at the library, the D-25s is portable, since it is small and light enough to easily carry. It has also been stated that the proprietary battery leaves much to be desired, so for this definition of portable, the D-25s can be said not to be an ideal choice.
If by portable you mean small enough to fit into a bag or in your hand, taking up little counter space and use in an environment where you have access to an AC outlet, the D-25s is quite portable, and can be used as a small bedroom source, to take outside on the patio, use at your desk at work, or take to the library etc.
IMO, since these are NOS players, and are known to be a bit twitchy and fragile, I would not use them as source that I moved around frequently. I would leave it in my house to use in those areas where I don't have access to my main rig, or use it at work where it can stay in a desk drawer.
P.S. I owned the D-25s, and I thought is was a good player, but a bit too warm for my taste.