NiMH batteries are great, they do have a slight memory disadvantage. It is one that only somebody who pays very close attention to their batteries will notice. When you use NiMH, use them until the GPSr or whatever device they are in automaticly shuts itself off, then recharge then per the manufactures recomendations. At work, I use NiMH batteries in my Motorola Minitor IV pager, they usually last 36+ hours of continous useage. The pager alerts me when they are low. According to the service tech from the local radio shop, only after the batteries are low should they be recharged. This was confirmed by the tech from Medtronic (The people who make defibrillators). As for my GPSr, I also use NiMH and follow the same guidelines. I have an eTrex Venture & the batteries last 24+ hrs, usually leaving the backlight on continuously (I take it to work & work @ night). They are the Energizer 2300mAh rechargeable that I picked up at Wal-Mart for 10.00 for a four pack. The charger is a 1 hour charger from Radio Shack.