What battery do I need?

[1970Thunderbird]

Hello all,

I'm about ready to put my 80hp Mercury on my boat and take it out. Before I can do that, however, I need to buy a battery.

I know there are several different battery options: dual purpose, deep cycle and what not.

How do I choose the right one? Any recommendations? How many cold cranking amps do I need? I know many people have two batteries. Should I get one deep cycle and one dual purpose, or two of the same? If so, which type? How do I connect them so they both are charged?

At this point, I'll be running the basics: the outboard, a stereo, and maybe a few gauges. I'll also be running lights when necessary, and perhaps a q-beam fishing lamp if I do some night fishing. I won't be using a trolling motor.

I'm open to any and all suggestions. I've heard I should use a dual purpose for starting the motor. Thoughts?

Thanks!

 

[roscoe]

Re: What battery do I need?

A starting battery for starting, gauges, and the navigation lights.

400 cca or 550 mca is all you need to start the motor. I doubt you will find a marine battery any smaller than that.

A deep cycle battery for all other accessories.

 

[onmedic]

Re: What battery do I need?

im being told to stay away from the deep cycle stuff. use only marine batteries. If you plan on using your electronics alot and not running your 80hp (no charge back to battery)then a deep cycle is fine. If your don't run that battery down significantly and then give it charge you will be shortening that battery life substantially.
I would have two batteries. A starting battery and another one for my electronics. i would isolate the two, weather you just wire your positive and negative from motor to one battery or use and isolater switch that allows you to choose battery 1, battery 2 or both, or off. I like option 2 because you can charge both batteries while your main motor is running if you want or just use charge one at a time. The OFF, is the best idea on this. Get into the habit of switching it to off , then it doesn't matter if you leave your key turned on, radio on, something like that. If you do happen to leave it all on, then battery 1 is dead but with a flip of the switch, battery 2 is good to go.
Your not isolate your systems this way, just which battery runs your systems.
This has not come from experience, just new to this, it was the most highly recommended way to do it. So far so good for me, not a lick of trouble nice and tidy, works well

 

[NYBo]

Re: What battery do I need?

im being told to stay away from the deep cycle stuff. use only marine batteries. If you plan on using your electronics alot and not running your 80hp (no charge back to battery)then a deep cycle is fine. If your don't run that battery down significantly and then give it charge you will be shortening that battery life substantially.

I think you have either been misinformed or have misunderstood what you've been told. A deep cycle battery can tolerate being run down significantly, but it doesn't require it for long life. It does require recharging soon after discharge for maximum life, just like starting and dual purpose batteries.

 

[onmedic]

Re: What battery do I need?

What i was told is that the deep cycle doesn't do well with little bits of charging all the time. Its designed to go way down, then be brought back up fully for maximum life, deep cycled.
Is that not true?
I'm running one deep cycle right now and one marine starting battery.

 

[SteveRoss]

Re: What battery do I need?

Hi Thunderbird...

Well, the experts and old timers have pretty well sorted out the type of battery you need, but I have an opinion on the brand.

If you are cost conscious, like me, check out Interstate Batteries. They are a pretty good brand, normally expensive and have a complete line of starting, deep cycle, etc. in different sizes. If there's an Interstate distributor/warehouse in your area, call them up and ask if they have any "Blems". These are slightly scratched, dinged or whatever, but are perfectly electrically good. I got my deep cycle battery for about half what it would have cost at a retail place. And it came with the full warranty/replacement guarantee !!

 

[1970Thunderbird]

Re: What battery do I need?

Thanks for all the help.

I'm gathering I should just use two marine batteries, somewhere in the 550cca range.

I was just going to get some at Autozone, or maybe some interstate batteries and use an isolator. I also have a solar charger I'll use to keep the second battery up to snuff.

 

[bruceb58]

Re: What battery do I need?

What i was told is that the deep cycle doesn't do well with little bits of charging all the time. Its designed to go way down, then be brought back up fully for maximum life, deep cycled.
Is that not true?
I'm running one deep cycle right now and one marine starting battery.

Not true. Any lead acid battery that is run down more loses its capacity. The more its held near full charge the better. A deep discharge battery can just handle the deeper discharges better. You never want to discharge a deep-discharge battery where it has less than around 40% of its capacity left.

For the OP, he doesn't need a starting battery because the current demand from a 80Hp outboard is small. Any deep discharge battery will be fine.

If you really feel you need 2 batteries for redundancy and safety, just get 2 deep discharge batteries. I would just go to Costco and Wallmart and buy what they carry and you will be fine for your use.

 

[roscoe]

Re: What battery do I need?

Not true. Any lead acid battery that is run down more loses its capacity. The more its held near full charge the better. A deep discharge battery can just handle the deeper discharges better. You never want to discharge a deep-discharge battery where it has less than around 40% of its capacity left.

For the OP, he doesn't need a starting battery because the current demand from a 80Hp outboard is small. Any deep discharge battery will be fine.

If you really feel you need 2 batteries for redundancy and safety, just get 2 deep discharge batteries. I would just go to Costco and Wallmart and buy what they carry and you will be fine for your use.

Its not any cheaper to get the wrong battery. Why would you tell him to do that?

 

[bruceb58]

Re: What battery do I need?

Its not any cheaper to get the wrong battery. Why would you tell him to do that?

A deep discharge battery will start a 80 HP outboard just fine. No need for a starting battery that will fail when discharged too much after only a few times.

I use a deep discharge battery to start a 454 engine! He will be more than fine with his outboard and it will last longer for him.

 

[montanajohn]

Re: What battery do I need?

A deep discharge battery will start a 80 HP outboard just fine. No need for a starting battery that will fail when discharged too much after only a few times.

I use a deep discharge battery to start a 454 engine! He will be more than fine with his outboard and it will last longer for him.

I have a 1977 Ford 188 HP I/O.

I wonder if a deep cycle will be good enough for starting and gauges, and need replacement less often. (Around here I have heard the suggestion to replace the battery every two years.) And does the typical charging system work as well for deep cycle as for starting batteries?

 

[bruceb58]

Re: What battery do I need?

I use them on my boat and I have a 7.4L engine. The charging system has no idea and doesn't care what battery is on there. Batteries should last 5 years if they are always stored in a charged condition and never discharged more than 50%(deep discharge only).

 

[montanajohn]

Re: What battery do I need?

I use them on my boat and I have a 7.4L engine. The charging system has no idea and doesn't care what battery is on there. Batteries should last 5 years if they are always stored in a charged condition and never discharged more than 50%(deep discharge only).

I appreciate the quick response, and will go for the deep discharge battery. Flathead lake gets some terrific storms. My concern is being dead in the water, between four foot waves with no room to leeward.
Any brand recommended? Thanks.