I have the same problem many people are having with their m200 Sansas. that half way through a song or at random intervals, it just shuts down for no apparent reason even though the battery is full and it works fine when linked to a USB.
I have a hypothesis that I think is right, you can test this if you want. Just for temprature reference I’m in Cheyenne, Wyoming.
It wouldn’t run with the battery that I had in my m250 yesterday, nor would it run on a battery in the upstairs of my house.
however, upon putting a slightly cooler battery from the basement in it, it worked fine.
this makes me also wonder about when i bought it, which was in december. at that time it worked perfectly, however it was usually a chilly 40 degrees outside.
I think that what the m200’s are suffering from is overheating. if anyone with the same shut down problem can attest that it was warm or roasting inside or out, then we may have a solution.
stick your batteries in the freezer. now i know thats a stereotype (and false with modern batteries) that will extend your battery life, however because it’s a heating problem if the battery is cold then it should allow the system to work even on the hottest of days.
thats the theory anyway. you’re welcome to try it or prove me wrong.