Another charging question (Oregon 600)

[ScotRoutes]

I've recently read that the internal battery charger in the Oregon 600 can be fooled into thinking there's a Garmin NIMH pack on board by sticking a bit of plastic into the battery compartment (it holds the switch down). That means I can now charge my own NIMH batteries in the Oregon. The Oregon also works fine while this is taking place. I was just wondering if anyone has experience of doing this; what the potential downsides are - and, assuming I connected it through a regulator of some sort to a dynamo, would this let me trickle charge the Oregon all day so that I could just switch on to lights when it got dark? That seems like one set of AAs would last indefinitely.