Surgeonfish,
as far as i excperienced the problem are the converters transforming from 110V to 220V as the may don't have enough power to feed the attached device.
Especially older 110 to 220V convertes would not charge the batteries 100% full or it takes very long to do so.
220V to 110V converters should not have this problem and the reason that they should be used only for 45 minutes is that they -cheap ones- may overheat
on long use.
Anyway, as Cary Dean already mentioned, newer chargers are multivolt and you can verify that on the charger itself where th input voltage has to be written,
but it may be difficult fo find in the confusion of icons and warnings...
In any case it should looke like this: Input Voltage 100-220V ~
If there is written only 100V ~ then you NEED a adapter, otherwise you will kill your charger!
If you need a adapter/transformer, get the biggest one you can buy, small ones usually break immediatly.
Depending on your charger, you may get a european or other 2 prong cable for it, you may ask S&S about that.
I use this Adapter and never had problems: http://www.swisstravelproducts.com/
Be advised that the programmer of the website must be blind.... 
The swiss power adapters use 3 prong plugs as well, but i had some problems with the third prong as well (before i used the Swiss Travel Adapter),
so i made it short and sawed away the 3° prong what is the ground. I belive that this prong is not used on modern electrical devices as it is the ground and today the ground is bonded to the negative lead/prong.
I made this modification on my own risk and and damage to me or the deveices will be 100% my own fault!
Don't do that if you are not knowing 100% what you are doing and are not willing to take the consequences of it!
Chris