500 ma should be just right for a small battery like that. I have burned up a couple of inexpensive power supplies like that. In both cases I am pretty certain I unintentionally had the polarity reversed. I knew to connect + to +, etc., but apparently misunderstood the markings on the power supply as to which wire was which. In one case I know that is what happened because I had bought two identical power supplies, cheap, like $2.95. After I burned up the first one I held my breath and tried the other one with the wires opposite. It worked. So either I misunderstood or the markings on the ps were wrong. Now I always double check with my DMM.