go into the backlight control thing in system
then on battery power tab untick the turn off battery light thing if device is not used for.....
then it should stay on all the time and kain your battery
or if the xda is charging while gpsing then go into the external power tab
do the same
if the box is ticked it will put a limit on before the light turns off
if its untocked it will stay on and draint he battery