I currently have a Merc 800 80hp that is started off of a "Starting battery". The boat is only 16 ft long, but I like to use the CD player, depth finder and my VHF radio while the boat if off. I usually do not have the VHF on continuiosly. Do I need to add a "Deep Cycle" battery as well or one of the "Dual" purpose marine batteries? I used the "Starting" battery last year, but I never kept the engine off for more than 15-30 minutes while I was listening to the radio. Any advice would be greatly appreciated.