I am planning on adding a 2nd battery to the boat. I was initially going to buy another deep cycle marine battery, but after reading some info on another site I found that I may want to keep the marine battery for my electronics and use a standard battery for starting.

I read that marine batteries are designed for a long slow drain and a slow charge. It said that a regular car battery would be better for starting.

So here is my question. Should I get a car battery for starting and use my marine battery for my electronics or should I get another marine deep cycle for starting also?

Yes I will install a perko switch either way....

Thanks for youhelp

What kind of engine are you starting?

Mike

why not get a marine starting battery?? You don't want to be firing up the motor with a deep cycle battery, it may work but the life of your battery will be pretty short.

I'll be starting a Chev 250....and as of yet my kicker does not have electic start or a charging system. Eventually it will, but not yet....

I ass-u-me-d that all marine batteries were deep cycle. Is that incorrect?

The "Marine-ness" of a battery isn't necessarily the same as its "deep-cycle-ness." "Marine" may also mean that the battery has SS threaded terminals for instance. Also, deep-cycle is not a true/false sort of thing. There is a spectrum of "deep-cycle-ness."

BTW, just having an Off-1-2-Both switch doesn't provide any real isolation, since you have to put the switch in Both to charge simultaneously, or keep fiddling with the switch. To get the full redundancy benefit of 2 batteries, you would need a dual-output alternator and an isolater. $600 later ...

You may want to consider a single large spiral-cell battery like the Optima D31M -- lightweight, compact, plenty of cranking amps, plenty of capacity, no switch to fiddle with. Yes, if you leave the lights and electronics on for a long time without the engine running, you will drain the battery and be SOL.

Just went through this recently and talked with some elecronics specialists. As the above thread states, it can be very difficult/expensive to totally isolate your two batteries. You do not always need a starting battery to start your motor/engine. If your starting draw is relatively small a regular deep cycle will do just fine. It was pointed out to me that the most important thing to have were two large(29-31) series batteries both in equal condition. If either battery is in a weeker condition it will draw down the other battery constantly and you will end up with two shot batteries. My .02 is to buy matched batteries and a battery strength indicator. This setup has worked very well for me and has taken all of the guess work out.

Salmon Stacker:

I have a custom made boat, had the 2 batteries placed up front, for better weight distribution. Then I had them put a control, where I could run off 1 battery or the other, or both.

Now here the part I like, spent the money and got 2 of the "new jell filled" deep cycle batteries, can't spill any acid. Believe me, you can start your motor and run an electric motor.....with just deep cycle batteries. Matter of fact, it is recommended that you have 2 batteries that are the same.

"Worse day sport fishing, still better than the best day working"

another thought,
on my boat I have 2 batteries, 1 starting and 1 deep cycle. I have the starting hooked up to the outboard and it also supplies power to the items that are on my control pannel, lights, wiper, horn, bilge pump. On the deep cycle, I have all my electronics and down riggers. This battery is hooked up to my kicker for charging. I don't have the batteries connected. I do have a set of inexpesive jumper cables in my boat in case I ever need to jump one to the other, but never have. Both charging systems and batteries are isolated from each other and no swithces or isolators to worry about.

Thanks for the all the input.

I like what baddawg has done. I think that I would change it so that the electronics run off of the deep cycle battery that also starts the main engine so that I can go out crabbing or just go for a ride and still have use of my elecronics without worry of draining the other battery. I wouldn't want to have to start the kicker motor so that my fishfinder will work.


Until I get a kicker that has a charging system it won't work for me, but when I do I think that is a good way to go. So until then....Well... not sure. Any other ideas or input.

go ahead and give it a try! You will find that if you throw a charger on your deep cycle you will be able to run your electronics and downriggers for several days with no problems and no need to recharge.

Isolators are not all that great, you will lose about a volt across one. Wich means that your alternator is putting out 13.5 to 13.9 volts to charge your 12 volt battery to 12.8 volts. Given tose standards it is pretty hard to get a full charge at 12.5 to 12.9 volts under normal circumstances. The best compromise may be a 3 position battery switch. Leave it on both while the alternator is charging and if you plan on a load for awhile with out running the alternator then switch batteries accordingly. I will be going to 2 golf cart 6 volts in series for my deep cycle bank ( house batteries), and keeping my starting battery just in case. the two six volts are replacing my single deep cycle only because we overnite on the anchor occasinaly and I want an inverter to make coffee with...other than that I have had great luck with one deep and one starting battery on a three position switch. This is by far not you only option. And if you think you might forget and leave the battery switch on both when you shouldn't then this set up definitly is not for you...

Buy the 12 volt bible...or 12 volt boaters bible...its out in my boat right now and I am not going to go get it... ..
It addresses all of these questions and gives you solid answers and explanations for those answers. And it is not some huge 3,000 page tome you cannot find anything in. Its a couple hundred pages, very easy to understand common sense. You will not regret this book...mine spends more time loaned than it does with me!
I am sure Amazon has it and I know BW and WM both stock it

I isolated the batteries by wiring a seperate fuse block ($12) to a costco deep cycle group 72 that is charged by my Honda 8 kicker (puts out 5 amps) and runs all the accessories that may run my battery dead eg; lights, stereo, amplifier, cigarette lighter adapter etc...

For starting the 302 I have an Optima gel starting battery, also from costco, that runs the starter and critical acc like bilge pump, wipers, sounder, etc...

works great

I can charge or jump either battery with jumpers if need be.

ps; I choose to wire the electronics to the starting battery because they use so little power and that battery is always tip top while the deep cycle may get run down after I pass out and leave the stereo on or something like that and a run down battery is not good for electronics.

I resemble that remark

This is why I got away from switches and multiple batteries -- I just could never remember to move the switch out of Both, so I ended up running as a single large battery anyway.

SalmonStalker, lot's of great advice given.

When you're ready to purchase the battery(s), if you're put off by the price of gel-type, take a look at the TROJAN brand, group27 marine batteries. Rugged and fair price; popular battery around here.

Thanks for all of the input. I appreciate all of the input. You guys have given me a lot of good ideas. Now to go get the battery and figure out how the heck I'm going to set it up.....

finegrain... I bought a 6" diameter screw in hatch with a clear cover, moved the battery switch to an area that had enough room behind the bulkhead fo the switch and enough room on the bulkhead for the cutout and hatch, Even backlit it with a red l.e.d. off my courtesy lights! Now even if I forget the thing is right there staring at me and with the back lighting I at least remember when it gets dark and I turn on the courtesy lights.

SS another option is 2 series 27 deep cycles of the same lot and if possible consecutive serial #'s, hooked parallel. A lot of what I look at for myself is more for spending the night (or 2) on the batteries. If you are going out for the day and running an alternator or putting the batteries on the charger at the end of the day, your six cylinder and two 27 deep cycles makes a lot of sense to me

One thing i remember is try to never let the voltage drop below 11.3(?) volts. If it drops below that it is considerd one cycle. Deep cycles are rated on reserve minutes( #of minutes at a 25 amp load before the voltage drops below 11.3 ???) and cycles, Keep the voltage up (by adding batteries or going to a battery that has a longer reserve) and the cycles are not nearly as important.....