The Outdoor Line Forum

My boat needs new batteries. Right now it has a dual battery setup. A starting battery on the First circuit of the battery switch and a Deep Cycle battery on the second . My boat does have any large draw Items minus two Scotty electric downriggers. The Normal Fish Finder, VHS, Stereo. I dont have an inverter or Fridge stuff like that. The second battery, should I still use a Deep Cycle battery or go with a second starting battery? I also have a Yamaha 9.9 Electric start that charges batteries. It is wired to charge the battery that is selected by the battery Switch.

I believe you should have a good starting battery isolated just for the two motors and a good deep cycle for the "house". Keep all electronics, downriggers, stereo etc connected to the house battery and away from the starting battery. The trick with the deep cycle is going to be charging it, it will take longer to recharge. Depending on how much running you do you may not get a full charge on the deep cycle. If your boat sits in the driveway a fair amount I would recommend a onboard charger that you can plug in while it sits.

Hey LM,
I'm a boat-head (my pards might have a different term for my afflictions...) and I love these types of questions!

Before suggesting a specific battery, we need to talk a little battery type or more correctly battery technology. These days we have four basic types of marine batteries available to us. In order of cost per amp they are:
The common automotive or "flooded cell, AGM or "Absorbed Glass Mat, Gel cells and dry cells.

Of these options the best choice balancing cost, durability and power, the AGM is the leader of the pack!

Whereas a flooded cell lead/acid battery has plates that are merely suspended in a solution, an AGM batteries plates are supported by a fiberglass mat which is saturated with electrolyte, resulting in a battery construction which is very vibration resistant as well as sealed to prevent leakage. One of the largest benefits of going with a pair of AGM's is the fact that they function as both starting and deep cycle batteries so you really can't go wrong!

Whichever type you choose, do not mix battery technologies in a installation as each type has its own charging rates and requirements.

Finally, you should consider an on-board shore power charging system such a the Minn Kota Digital on board. Not only will your batteries remain fully charged but their life will be extended as well!

I have been putting deep-cycle batteries in boats and RVs for years. I never seem to get more than a year or two out of the batteries. I even bought a higher end Trojan that didn't work for too long. When I bought my boat in 04 it came with Interstate batteries (one cranking and one deep-cycle). I just had to change the deep-cycle last fall, and the cranking is still running fine. I now have Interstate batteries in everything. There may be better batteries/technologies out there, but based on price vs. performance I am sold on Interstate! Also I have invested in a float charger to keep them fully charged while it is sitting in the garage. I rotate it between the deep-cycle, cranking, and the Harley.
L8R
Dan