Battery decision time???

emilime75

Petty Officer 1st Class
Joined
Jun 23, 2009
Messages
204
I am in need of a new battery and was considering my options. I will be completely rewiring the boat so I could go 2 ways here.

First option is a single starting battery that will also be used to power the bow and stern lights, a cd player, a GPS and a depth gauge.

Second option would be dual batteries (one starting battery for the motor, and a deep cycle for the stereo, GPS and depth gauge).

The motor is a 77 Mercury 115hp outboard. I was wondering if the charging system on this motor was sufficient to charge 2 batteries at once, or would I be better off charging just the starting battery from the motor and charge the accesory battery at home?

How many hours of operation can I expect from a new deep cycle battery on a single charge used to power the accesories mentioned. I know this will vary depending on size of battery and other conditions, but I was wondering in general terms using a typical deep cycle battery in good condition and fully charged.
 

Laddies

Banned
Joined
Sep 10, 2004
Messages
12,218
Re: Battery decision time???

A 2 battery option would be better but use a battery isolator in the system so that the start battery is always charged first.
 

emilime75

Petty Officer 1st Class
Joined
Jun 23, 2009
Messages
204
Re: Battery decision time???

Thank you Laddies. So your suggestion would be to use 2 batteries, and have them both wired to the charging system of the outboard with an isolator between them?

What about the starting battery vs. deep cycle battery? Should I use a starter on the motor, and a deep cycle on the accesories? Or would 2 starting batteries be fine? I read somewhere that if more than 1 battery is used they should be the same type/size/age, but that article did not incorporate isolators.
 

Yepblaze

Lieutenant Commander
Joined
Jun 1, 2001
Messages
1,686
Re: Battery decision time???

You will only NEED one battery for your needs.

A dedicated Deep Cycle battery is not what you want to use as they (by design) do not have the cranking voltages you would like to have for starting the motor. Perhaps a dual use Cranking/Deep cycle would be ok.

You will find that the charging system on that motor to be (barely) adequate for running lights, a fishfinder, GPS, and a stereo of low to moderate power. Although once charged and at full running speeds you may experience voltages above 18 volts.

I've been running one battery (dual purpose) on mine for years without issue. If I have additional electrical needs for an outing, I bring along another (dual purpose) battery and just run it, stand alone, unhooked to the boat's system and charge it back up when I get home.
 

emilime75

Petty Officer 1st Class
Joined
Jun 23, 2009
Messages
204
Re: Battery decision time???

Yepblaze, I wasn't thinking of using a deep cycle as the starting battery. My intentions were to use either one starting battery, or a starting battery for the motor and a deep cycle for the accesories. My concern is that we plan on using the boat to seek quiet/calm swimming spots and anchor for several hours at a time. This is when the stereo will be used, but during this time it is the only electrical item that will be used. That said, I also don't plan on using the stereo while the motor is running. The stereo will consist of a CD/AM/FM head unit and 1, maybe 2 pairs of speakers. I don't plan on using an amplifier at this time.

Do you still think a single battery is all I need? Somehow I'd be concerned that after having the stereo playing for several hours, a single battery would not be sufficient in starting the motor.
 

Bifflefan

Commander
Joined
May 27, 2009
Messages
2,933
Re: Battery decision time???

A regular batt is for starting but it cant really handle a constant drain for long.
A deep cycle is for the constant drain, but isnt really good for starting (altho I use one for starting).
The charging systems on an outboard are not that great, they can charge up the batt but thats about it.
I do like the two batt systems (puting it on this winter). Im going to have the starting batt and a separat deep cycle for running the other stuff except the lights. that way i can run what ever untill the batt is dead and not worry, then just charge it when im home and let the motor charge the starting batt.
 

milehighboater

Petty Officer 1st Class
Joined
Jul 28, 2009
Messages
235
Re: Battery decision time???

I love my two battery system. I have cranking and lights on one battery and everything else on the deep cycle. My merc doesn't have the chargin capacity for the deep cycle so I added a two battery on board charger/maintainer and it works great. After I get off the water I just plug in the boat and leave it alone. As far as getting a deep cycle to power everything and for how long, this is a good site to convert watts to amps to figure how many amps you are using per hour. http://www.powerstream.com/Amps-Watts.htm
just add them all up and get a battery to match. But just as a standard I have a 600CCA and it powers a CD player, fish finder, trolling motor and livewell all day no problem. I am running Interstate batteries and they are great, I got almost 8 years out of my old deep cycle from them and they are worth every dollar. And really the deep cycle was only 98 dollars when the wal-mart brand was 79.99. Interstate was worth the 30 bucks.
 

Bill Kilgore

Petty Officer 2nd Class
Joined
May 15, 2009
Messages
145
Re: Battery decision time???

I think you will do best with dual batteries. I noticed a rewiring project in your future. Two additional steps that may help your overall project is to:

#1 add a battery disconnect switch / switches. I am currently using the following one from here at iboats.

Our Price: $20.95 - Mini Battery Switch, On-Off - BEP Marine
Compare at $26.99
You Save: $6.04
(22% Off)
Part # 701
Low Price Guarantee

BEP Marine
mini battery switch

# 2 install an onboard battery charger. I have used the following charger for 2.5 years with very desirable results. Plug in and forget (except for checking water levels in batts once a month)

Our Price: $139.99 - ProSport 12 Generation 2 Onboard Battery Charger, 12amp, 2Bank - ProMariner
Part # 42012
This one is also here at iboats

I noticed that a local sporting goods store had 2 different starting batts on the same end cap. Both were marine starting batts

Batt A = 550 CCA = $54.xx

Batt B = 1000 CCA = $59.XX

Five or so bucks for 450 CCA's seems like a good deal.
 

emilime75

Petty Officer 1st Class
Joined
Jun 23, 2009
Messages
204
Re: Battery decision time???

Thanks for everyone's input. I think the 2 batteries will definetly be the way to go. I will use a starting battery for the motor and possibly running lights, and a deep cycle for the rest of the goodies.

That brings me to a second question. My boat is a 17' ski boat. I have ample space in the rear starboard side of the boat, but I was considering placing the batteries in the bow. The boat is a closed bow but there is a sizeable access panel and the batteries would fit well in that space. My thought for placing them in the front is weight distribution and I thought it might help with getting the boat on plane quicker. My other option would be to place them where the current battery is now, rear starboard corner opposite the 18 gallon fuel tank on port side of the boat. What is more important, side to side wight distribution or front to back? Some things to consider are that the driver's seat is on the starboard side, so there is some weight usually there anyway to offset the fuel tank and fuel, and then the fuel tank itself...the weight of it will vary depending on how much fuel is in it.

Am I just putting too much thought into this? What do you guys think?
 
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