My guess is that you won't have problems with NiMH batteries and probably won't have any problem with alkalines. I have an old CCrane trek lite that is similar. It does, however, have a 10 ohm resistor between the 3 batteries and the LEDs. This obviously doesn't limit current, just drops the voltage a little. This light came with 2 LEDs, I added 2 more (existing holes in board). One LED did burn out after extensive use (several sets of lithium AAs). I haven't gotten around to replacing it yet. I'm using NiMH batteries for about 3.7v most of the time. the light is brighter with AA lithiums, but that is what burned out the one LED that failed. Note that the newer CCrane lights have a circuit in them. Apparently they thought it was worthwhile.