Fish-Hawk.Net

I started having some issues with my main battery last year and I'm looking for some advice. I've recently upgraded the main sonar unit to an HDS-7 and after a long day on the water without running the motor a lot I can drain my cranking battery. Not sure if it was the sonar upgrade or maybe just time for a new battery but either way, limping back to the launch with the bow mount sucks. The current battery came with the boat, it's the largest Interstate marine cranking battery with 1000mca but it's at least 3 years old and I know I've discharged it more than a few times. I just ordered a new 3 bank charger to make sure I keep a good charge on the main battery this year but I'm pretty sure I'm going to need to replace the current battery.
What I'm wondering is if I'll be better off with a dual-purpose cranking/deep cycle for the main battery? I've heard some mixed reviews on dual purpose batteries and just wondering if any of you guys are running these. Right now I'm looking at the Optima D31M which puts out 1125 mca and has 155 min RC. The other option would be to put in a third deep cycle just for electronics and just replace the main battery with another cranking battery. I'd really like to avoid having 4 batteries if possible so the dual purpose is looking pretty appealing. Any thoughts?

Thanks

I am also interested in this issue as I have 3 sonar/GPS units running off the starting battery as well as livewell pumps and bilges. Last year I had to buy another 31 series to replace the 27 series that I was using because I killed it. This year I am upgrading from 24v to 36v on the bowmount so I need to buy another battery anyway. I was thinking of using another 31 but some have advised me not to.

It sounds like a new battery for the boat is in order. There are 2 rules when it comes to batteries.
First, you will never be sorry buying one that seems like overkill [too high a rating]. Many people get mad after the fact because they could have for a few more dollars bought a more powerfull battery.
Second, never use a deep cycle battery to start the engine, it will kill the battery in a short time. Starting batteries require high output for short periods of time. Deep cycle batteries feed smaller amounts of power over a longer period [trolling motor].
You can buy a deep cycle/starting battery with the highest output and this will serve you well if properly cared for. Charge after EVERY use and don't completely discharge them.
...Larry

Dual purpose all the way. Nowadays, we've got aerator pumps, radios, lights,sonars, sonars and more sonars, all running off the "cranking" battery.

My last two have been dual purpose and have never required charging except during the winter.

Yeah, dead-on-the-water cranking batteries sure suck but that's how you learn your lessons!!

GT