A cordless electric will go through a few charges(batteries) before it could do significant damage to water on the court. A corded unit would be stronger and more effective, but dealing with the cord is a pain. Gas would be the most effective, but carries its own problems(might not even be allowed in some areas).
Having said all that, I've owned Black and Decker 18v cordless blowers for years and it wouldn't hurt to have one+ handy. They are readily available, batteries easy to find and other tools can operate off the same power source. Just don't expect TOO much
. Shop for a lower price, perhaps a free extra battery(from Lowe's on occasion)...
I've seen a half-dozen blowers in use on ONE court and it still takes a while to have any real effect.
A rolling leaf blower(gas) would be the most effective in moving air across the court surface, but that's an entirely different kettle o' fish