Battery advice for a rookie

I've found this site to be a HUGE help for a first-time boat owner, but have one question I can't seem to answer from previous posts. I just bought a 15.5' aluminum fishing boat with a 40 hp Johnson Tracker outboard (1989) and electric start. I have one very reliable dual purpose marine battery with 850 mca/180 reserve capacity that I plan on using to run the following:

- bow-mount 50 lb Minn Kota Power Drive
- Bottom Line 4800 depth finder
- live well pump (when necessary)
- bilge pump (rarely -- no leaks)
- running/nav lights for later in the day

I am fairly confident my dual purpose battery will handle the trolling motor/etc load for a day -- I never go out for more than a day without charging at the cabin/home overnight. Am I right, or a little overconfident? Also, what kind of starting battery is necessary to consistently start a 40 hp outboard? Is a marine starting battery necessary, or can I use one made for automobiles? I don't have lot of extra money, but I also want to buy something that won't leave me uncertain about making it back home, or buying a replacement battery after only a year of use...

Thanks for any insights anyone out there may have!

Re: Battery advice for a rookie

Make sure you can cold start that motor with a rope before powering it with your cranking battery. Your alternator will not be able to replace all the amps used by the trolling motor.

The battery you have will do either task (cranking or trolling) adequately, but I highly recommend adding a dedicted deepcycle for trolling. Accessories on the cranking batt are fine. I use an interstate deepcycle for cranking, first one lasted nearly 5 yrs, this one is on yr 2 and going strong.

Always recharge your trolling batt soon as you can, any time spent at less than 100% state of charge will shorten its useful life. Top your battery's off every month or so if they don't get used, or else get a "smart charger" with "maintain mode" and leave 'em plugged in when not in use. Not a "trickle charger".

Marine batteries are made tougher to take the pounding they get in boats, some people use automotive, but I don't.

Re: Battery advice for a rookie

the 40 is not that hard to rope crank in an emergency. practice it at home on muffs. then when the $$$ get a little freer i use a battery that is compatible with my tow vehicle, for a starting battery.

Re: Battery advice for a rookie

Yes, of course I should be testing the pull-start -- can't believe I hadn't thought of that! I've got the muffs, and will be sure to give it a shot as soon as the weather warms a bit. I guess the rope-start option is one advantage for us low-hp guys...

I have been taking good care of my battery, keeping it charged every month all winter, plugging it in the second I get home from a trip, and so on. Unlike some of the jokers I've seen around here -- leaving their batteries out all winter (in Manitoba, probably one of the coldest places in Canada), charging them only a couple of times a year -- I don't have the money to be that negligent.

Thanks again for the help. This site is a life (and money) saver!

Re: Battery advice for a rookie

I am a rookie also and just bought my first boat. I purchased a Alumacraft 160 Fisherman. I installed a bow mount trolling motor and have a deep cycle battery for the bow mount trolling motor. I also have a transom mount trolling motor and I want to use a Optima dual purpose battery for my electric start motor and trolling. Will this be good for a full days trolling and starting my 25 HP Yamaha?

Does the Outboard have an alternator that charges the battery while it is running?

Thank you in advance for your answers.

Re: Battery advice for a rookie

Its confusing when you hijack a thread.There is a new thread tab at the top of the electric/electronics page.Check the voltage at the battery with the motor running at 1500 to 2,000 rpm if it charges should be about 14+ volts
It will only maintain the battery under normal use.What ever battery you use
you will need to charge within a reasonable time as possible after trolling.Without knowing the battery rating and the size trolling motor its difficult evaluate your setup.
also would be good to estimate the actual trolling motor run time.

Re: Battery advice for a rookie

Sorry, I didnt mean to jump in on his post. I fugure someone would give me some grief about asking a question that had already been answered. I have an Optima D 34 M dual purpose battery and a 55 lb Minn Kota Endura. I usualy only use it 3 hr max off and on during a fishing trip. I also have a deep cycle battery for my bow mount 55 lb Power Drive V2 with CoPilot that I can use too.