I just purchased a Roomba Discovery SE robotic floor vacuum from the
states... However i live in Germany.  The problem is that the wall
charger unit is rated at 120V/60Hz and German Power outlets are
220V/50Hz.  I could use a Power transformer, but mine draws 300 Watts
(most of that power is just wasted because the charger doesn't need
that much).  I would like to know if there is a battery charger i can
purchase that is dual voltage (110/220V 50/60Hz) or if not then is
there a 220V version?

Your transformer is probably rated at 300 wats. That means that you
can draw up 300 watts through it. If you hook up the Roomba charger to
the transformer it will only draw slightly more current that the
charger its' self. Slightly more because transformers are about 98%
efficient.

Just to ?second source? anotherbrian info for your peace of mind. It
will be just fine.

But to expand slightly, a transformer is not like a light bulb or a
heater, where the wattage is a rating of how much power they will
consume and radiate. If there is no load on a transformer it will draw
very little power -- only a few watts maximum. When it is loaded it
acts as an efficient ?conduit? for the power and doesn?t itself use
power or heat up -- apart from slight efficiency loss.

Best

I also recently bought a Roomba 120V in the States with a cheap
transformator (120-220V) so it could be used in Europe. In principle
this should work without
problems if the Roomba fast charger was a "normal power converter"
from 120-22W. However I doubt this, and I in my case the fast charger
also ceased to work after a short while. So you might experience the
same problem. However, you also might be lucky it just works.
 
I am now trying to find somewhere in Europe where I can buy an
European fast charger. Any suggestions.

Ole