SENKOMEISTER

I have a 16ft Tracker boat with a 9.9 horse Mercury. Instead of the deep cycle battery and starting battery, I wanted to just have 2 deep cycles for when I go for long weekends without any way to recharge. The deep cell will start my little motor, but if it's hooked up to the motor, will the alternator/charger in the motor do damage to a deep cycle battery? The guy at Bass Pro wasn't sure, but said to just disconnect the battery after starting before running up the lake. I can start my little motor with the pull cord if I want, and just keep the extra deep cycle as a backup, but I don't really want to be screwing around with wires every time I start and go somewhere with the gas motor. Anybody got any input?

I can never figure out overdrive or not. I have a V-6 Xterra Sport towing a 17ft aluminum Tracker bass boat. I switch the overdrive off on the back roads and smaller highway stretches, but when I'm on straightaway mostly flat highway for long stretches, I switch the O.D. back on and she cruises just fine. I hate to see the RPMs up high with O.D. off for long stretches. Am I asking for trouble, and why?