Jeff is right, a welder does boil water fast. I found it did work pretty well and fast but it uses a lot of electricity and you have to put water in often. Kind of looks like you are at Yellowstone park when it is running - lots of bubbles and steam.
As far as the 200 amp setting, I do use it a lot of the time, particularly when starting a new piece. I do watch the meter and switch it down to the 40 amp setting when it draws 20 amps or more.
The only problem I've seen with the charger at 200 amps is that it burns out the little bulb behind the meter a bit faster. No problem though, it is a standard automotive bulb that just plugs in.
Tom