MP3 players

I want an MP3 player. I already have two (well, one; my first has been snaffled by Şencan for her walks into work).

My current player is an Alba MP34GD11. This small unit is powered by a AAA battery, and it has an SD Card slot that can be used to expand the number of MP3s carried. Unfortunately for some reason playing from the SD Card uses the battery up rapidly; so rapidly, in fact, that I fear there must be a problem with this particular unit.

The player has suffered a little, especially from a drop onto a conveyor belt at Debenhams (yes, I do occasionally buy non-walking clothes). It is still working, but it is about time that I look for something better.

So what do I need? Well, the vast majority of the time I use it is when walking or at camp. I can easily use it for ten hours a day whilst out and about. The other time I use it is when on long journeys in my car, connected to the car radio via an aux in.cable.

Given this, what do i think are my requirements? Being somewhat anal, I shall separate them into three priorities; 1 being the most important and 3 the least.
1: Long battery life. I want to go on multi-day walks in the wilderness without running out of battery charge. This basically means that it has to be powered by AA or AAA batteries, which can be bought in many shops. A rechargeable battery is not good enough as I am often away from mains power for extended periods.
1: Lightweight. I do not want to be carrying a heavy device around with me. My walking kit is heavy enough already.
2: Main storage. I want at least 4GB of storage. I have 61GB of podcasts on my main PC, including 4GB of music and 14.4GB of audiobooks, the latter mostly from Librivox. (*)
2. Extra storage. I would like the ability to insert SD Cards containing extra MP3 files. Using these, I can carry vary what I listen to on long walks.
2. Robust. At the very least it has to be splash- and conveyor-proof.
3: Unfussy interface. My current MP3 player has an interface that is exceptionally non-intuitive. I can just about cope with it, but something that did not require several incantations to God (**) in order to find the directory I want.
3. An interface that will allow me to control the MP3 player from my in-car radio system.
3. An in-built AM/FM radio would also be a bonus, but not vital.

Of course, the best-known MP3 players are the various flavours of Apple iPod. Yet I shall not be getting one, for it does not meet the critical requirement of running from AA or AAA batteries. Neither, unfortunately, do any of the other modern players that I can find. I cannot be the only user of MP3 players who spends more than a couple of days away from mains power.

So I shall probably have to put up with the wonderful idiosyncrasies of my current player. But if anyone is listening from any of the numerous electronics box-shifters, please see the above requirements as an outline specification for a new MP3 player target at long-distance sportspeople. You could even call it the i-Plod. Or perhaps not.

(*) It is hard to calculate the duration of all these MP3 files, and I could find no public-domain tools that does the job. At 128kbps (a decent, if not stellar sound quality), then 61GB would be about 44 days of podcasts if played continuously. This is a very inaccurate finger-in-air estimate, as many of the MP3 files will be 64-, 256- or variable- bitrate.

(**) whichever deity you believe, or do not believe, in.