Can't help with the laptop GPS, since I have always used hand units (Garmin 60csx latest one). However, in the area of batteries I might help.
Get some of the 2500 mAh Energizer NiMH and you will be amazed at the time they hold a charge.
My 60csx, with the backlight on full, will run for almost 16 hours; without the backlight on, over 25 hours. Alkalines...don't even ask.
