I run my depthfinder/GPS combo unit about 12 hours a day when canoeing.  A 12 volt battery will last me about 2 days.  I found that with a small (8x8?) solar charger from Cabela's I can alternate the batteries and they last through a 6-day a trip.  I always have one charging back at camp while using the other one.  Not sure how efficient AA's are at re-charging, but I'd think you could significantly cut down the number you take along.