yes you can tape of the third lead...
I would look into Dual Pro chargers(they have a sportmans series = Cheaper) I use them in my bass boat... very popular amongst bass boats who have 3 and 4 battery systems. Very nice product and excellent customer service....
also the reviews on the Promariner Prosports are horrible......
here is just a sample of bad reviews...
http://www.basspro.com/ProMariner®-P...97825/-1464912