bikergbr,
The beauty of the adventurer 3500 is the now replacable battery, in testing i have had as much as 10 hours play with backlight permenantly on, but with the sleepmode active (not tried as yet), i think it will probably gain an extra 5 hours.
A word of caution, there seems to be a software bug relating to the sleepmode, and it somtimes doesn,t wake up meaning a restart, but several members of memorymaps forum have posted possible workarounds while memorymap work on a software fix, but i,m still thrilled to bits with it.