I have a rechargable battery charger I brought from Europe which runs on 240v 50Hz.
If I plug into US 110 voltage with an outlet adaptor will I simply get a "half speed" charging rate - or am I missing something here?

You might burn something up. I wouldn't do it.

Yeah, not that I've tried it, but I do believe that even though it's a lower voltage you can still damage something if you don't use a converter...

Hmmmm...I dunno. I know the other way round is exciting - Mrs Zipper did it on a visit to London and blew up her hair dryer, but in reverse?

Anybody know an electrical engineer that can say for sure ?

Even an EE can't say for sure unless they know the internal wiring of the adapter. Not all of them are made the same way. Similar, but not the same.

I can tell you based on what I know of electronics, the most likely outcome is that it won't work at all. The internal transformer is going to step that voltage down to half of what is needed for the DC conversion, at that point the DC voltage regulator is going to open current flow wide open to get a higher voltage on the load, causing it to possibly burn the **** up, or it may just never satisfy the load requirements and your batteries never get charged.
I don't actually know how the adapter is designed, so that was a wild guess.

Thanks for that, Betty. Makes sense - I actually spoke (via IM) to an electrical whiz over in Europe and he gave me the same explanation!

I need an answer to this one too.

Kcurrin - seems little doubt that Betty is quite right on this one. The lower flow of current is not enough to make the internal transformer kick in and lower the voltage.

It's no biggy, Radioshack have a range of cheap chargers...and a step-up unit for around $40 that I may purchase for my 240 volt rechargable drill..