What size is your tank?
The Groco Sweetank is a great system that does work...but unless your tank is bigger than 30 gallons, you can prob'ly keep your tank odorfree without it by simply increasing the ventilation and using an non-chemical tank treatment--e.g. Odorlos or Raritan K.O.As for your questions about current draw etc, I think those will be answered if you read the installation, operation and maintenance instructions...which you'll find at http://www.groco.net/Service-Manual/Sec1-Sanitation-SM/STK-Info.htmIt only draws 3 amps, but it also has to run 24/7...so unless you have a means of keeping your battery charged, I doubt if you'd want to do that on a mooring.