Marine Electronics Forum - How many batteries

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View Full Version : How many batteries

06-04-2007, 10:21 AM
I have a 25' center console with a single outboard. I has 2 batteries as of now that need to be replaced. I will drain one in about an hour with my chartplotter, radio, fish machine and vhf on. My question is how many should I install? There is space for 4 so should I do 3 in parallell and one single? I want to be able to run all my electronics and a livewell and not have to worry about power.

06-04-2007, 10:31 AM
is your batteries starting type or deep cycle?

06-04-2007, 10:46 AM
deep cycle

06-04-2007, 10:50 AM
two is enough batteries for single engine...u can always get optima blue top instead of getting more batteries than two.

06-05-2007, 11:17 AM
I would go with a good starting battery for the engine since their life expectancy is much greater. Then two deep cycle
batteries for the accessories. I would prefer all AGM batteries and would want to have either dual charging circuits or
add an alternator isolator if needed to charge all batteries.

On a small boat I use two group 31 flooded cell deep cycle batteries to run a gps, f finder, bait tank and 24 v trolling
motor. All that was available at the time was the Walmart batteries for about $65 each good for two years use.
I will be upgrading to AGM batteries in the next week or so from Cabelas. I recharge after every day on the water
with a good multi bank built in charger. If you have separate charging available while running you can get by with
two batteries as long as their both capable of starting the engine.

My preference for two deep cycle batteries for the accessories is to prevent drawing them below 50% level. All
deep cycle batteries will last longer if you do not draw them down to far and can recharge them quickly after use.


06-05-2007, 12:17 PM
But don't use an isolator on the alternator to charge them both. That would require messing with the engine wiring and getting an extra cable back from the OB depending on how it is set up currently. And isolators have a built in voltage drop so your batteries won't get a full charge. A small combiner for about $50 from Jones Trolling Motor Services is a simple 3 wire installation from battery to battery.

06-05-2007, 12:45 PM
An hour with minor electronics on is way too soon to kill a battery. It may not be getting charged at all. I have 2 start for engine only and 2 deep cycle that only get charged at the dock. I can be out with one batt running electronics for 4-5hours and still I have 12.6v before I hook up the charger.

06-05-2007, 11:39 PM
yandina is correct about the voltage drop using isolators but let me clarify that each evening when i return to shore I recharge
all the batteries with a good quality three bank charger to top them off. A combiner can work too or you can have two or three
batteries in parallel and take your chances.

The battery or batteries you speak of in the first post are probably toast. I can run two 7" screens, 20gal bait tank, all day
with the 82 lb thrust trolling motor intermittently without problems. I don't think you should be able to see much of a drop
in charge after 8 hrs of using two screens. Your bait tank may draw a little more, but two good deep cycle batteries for all
of this load should last quite a while without drawing the batteries to low, that is what often kills them. I think a top quality
onboard charger will pay dividends for the long haul. And leaving the dock with fully charged batteries makes for a more
pleasant day on the water.


06-06-2007, 03:17 PM
Personally I would start with a good 27 group starting battery for just starting the engine. Then I'd go with a pair of quality group 27 6 v golf cart batteries in series for the house battery. IMO golf cart batteries are the most suited for the day to day drain/ charge demands placed on them. What brand of golf cart battery you go with is up to you, I've been running the same top of the line Interstate batteries now going on my 5th year and they still show zero signs of ill effect.
Yes with this setup you should run an isolator switch.....charge the starting battery on the way out and change the switch over to charging the house batteries on the way in...or something to that effect.

If you install the setup above and you still run into a problem then you have some sort of short to ground which is drawing a ton of power!

I know with my boat I upgraded my alternator (I have an I/O) to one that puts out probably more amps at 1400 rpm then yours does at WOT....your's is probably delivering between 25 & 35 amps at WOT, mine's doing that at around 1200 RPM, my max is something like 110 amps at WOT. I do not have an on board charging system (I trailer my boat) and therefore I wanted a charging system off the engine to give me what I need.......very rarely do I ever stick a charger on my batteries back at home...only when I know I'll be gone for a four or five day cruise will I and that is only to be on the safe pre trip maintenance.

Tip: High output alternators are very expensive so I found out; I had an alternator made for me at a shop which rewires starters and alternators for a fraction of the cost! Between $700 to $1,200 to buy new, I think it was $180 to have one made up for me. The one I had made for me would have been priced out around the $1,100 mark......that’s a serious savings!

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