I live in Australia (220-240 VAC, 50 Hz mains). On a recent trip to the United States (110-120 VAC, 60 Hz mains), I purchased some battery-powered tools that came with a charger. The charger has this printed on it:
I have a transformer for converting Australian mains to 110 VAC:
It is just a transformer, not a frequency converter.
Is there any reason to be concerned about putting 50 Hz AC into my new charger? My thinking is that there is not, because the charger is converts the AC current to DC anyway, before feeding it into the battery.
Problems with AC frequency have to do mainly with induction motors, I think. I found this question, and some others, that seem to confirm that.
I can open up the charger to see what circuitry is in there, but I'd rather not if I don't have to.