I use both. No question that you save money with rechargeables. However, I've noticed an inconsistency in the physical size of some of the rechargeable batteries from Empire. I have a pair that will somehow shift position slightly when installed in my GPS, and it turns off. You can feel the lack of tightness when you install them into the GPS or try to install them into the charger that came with them (I have to wrap a rubber band around them to keep them in the charger.

GPS works fine with alkaline batteries. FWIW, the Garmin Etrex CS seem to run forever on a set of either type.

Caruso