Northwood boat / 30 Hp Mariner motor

I've just purchased a 1995 Northwood fishing boat, a 1996 30 Hp Mariner motor and a 1995 Karavan trailer. I would like to thank everyone for all the helpful hints and stories. I have done a little work on the trailer and even changed the bearings myself! Thanks MarkC for the trailer link on bearings:<br /> http://www.rverscorner.com/articles/bearing1.html <br /><br />The questions I have are:<br /><br />1. The Hummingbird fish finder only works when the motor is running. Can I just disconnect it and run it straight off the battery?<br /><br />2. Does a 30 HP Mariner have an alternator to charge the battery?<br /><br />3. Should I have to charge the battery after every time out on the water?<br /><br />4. I thought the starter motor was starting to but now I think I need a new battery. How long should the battery last?<br /><br />Thanks