Battery Banks 90 HP Merc

[Eriespider]

I have a 17 ft lund with a 2 stroke 90 hp merc. I need a new starting battery. My current setup is a 12v starting battery in the back of boat for starting and accessories. I also have a 12v trolling battery in the front for electric trolling motor only. Only wired to trolling motor. I must charge this from battery charger at home. I have owned the boat for over 10 years, so naturally I have gone through 2 starting batteries and now I need a new one. This is expected with the time frame.

My on going dilemma! I use the 90 hp for trolling the Great Lakes for Salmon and Walleye. I will troll for as long as 8-10 hours on Friday, same Saturday and Sunday. By the second or third day my starting battery starts to weaken and a few times I have had to use jumper cables and jump start the starting battery from the trolling battery up front. This really makes me nervous 17 miles out in Lake Erie.

I expect the drain is from a combination of my accessories and the slow trolling speed not charging the battery back up. My accessories only consist of a marine radio, fishfinder, 2 big john electric downriggers and limited use of running lights early in the morning.

I rarely use the electric trolling motor, once in last five years. This battery serves more as an emergency backup.

I need suggestions on how to eliminate this problem. Do I install two batteries in the back? Parellel or Series? Switch? etc for starting and accessories. Do I install only one new starting battery in back and try to wire the front electric trolling battery into the equation? Where would accessories go? etc.

What would you do in this scenario?

 

[Silvertip]

Re: Battery Banks 90 HP Merc

You need to get the downriggers off the starting battery and onto the deep cycle trolling motor battery -- especially since you don't use it much anyway. Downriggers are high current draw devices which place an undo strain on the starting battery. Batteries should always be purchased with the highest capacity you have room for. The higher the reserve capacity or cranking amps the better. Deep cycle batteries are far better at being deeply discharged than a starting battery. Carry a jump start box as a backup if you still feel the need.