I carry AA NiMH spares. I make a point of not using the Oregon’s recharging function. It works, but I try to not make a habit. Simpler to carry NiMH spares.

The NiMH batteries that come from Garmin are in a sleeve that allows them to charge in the Oregon GPS. Other batteries can be used, but if they aren’t in the sleeve, the GPS won’t allow them to charge. The sleeve is what prevents someone trying to recharge alkaline or lithium primary batteries — the power won’t flow.