where does my negative go on dual battery

pitbulll · Apr 30, 2009

hey guys i think i know but want to make sure.im putting in a second battery on boat does my negative cable from the second battery go's to the neg. post off the first batt.then the neg.post off the first to the engine.is this correct

Splat · Apr 30, 2009

Re: where does my negative go on dual battery

Yes you can ground to either battery, then will ned to run a jumper from one negative terminal to the other nagative terminal. That way no matter with battery you are running off of the circuit is complete.

Bill

bowman316 · Apr 30, 2009

Re: where does my negative go on dual battery

but only do that if both batteries are identical.
If one is bigger, or one is a deep cycle then keep them isolated.
just have one back up battery, or a battery for accessories.
the way you have it, it will be one big battery, not 2.
so once it is dead, that is it.

Splat · Apr 30, 2009

Re: where does my negative go on dual battery

Sorry, double post

Splat · Apr 30, 2009

Re: where does my negative go on dual battery

bowman316 said:
but only do that if both batteries are identical.
If one is bigger, or one is a deep cycle then keep them isolated.
just have one back up battery, or a battery for accessories.
the way you have it, it will be one big battery, not 2.
so once it is dead, that is it.

Ummmmmm........ Close.....but let me see if I can clarify.

It willonly act as one large battery if the posative sides are also tied together in paralelle. Meaning both batteries will be drawn off of at the same time. If the negatives are tied together and you are connected to a battery switch you will only draw from the battery selected, or the battery your attached too.

If both posatives are tied together via a jumper then yes both batteries will be drawn from at the same time. A word of caution, tying 2 batteries in paralelle does not give you double the run time. More like 60-70 percent more, not true doubled tho. So running batteries one at a time hrough a switch is a better option. You'll get better run time, plus when one begins to wear down you know your half out of power.

Bill

Vic.S · Apr 30, 2009

Re: where does my negative go on dual battery

Batteries connected in parallel should be connected up like this with the supply leads connected to the negative of one battery and the positive of the other. It balances out the resistance of the connecting leads so that they share heavy loads equally.
As indicated they should both be the same type and similar if not the same size.

pitbulll · Apr 30, 2009

Re: where does my negative go on dual battery

ok i understand.i have a battery switch with bat.1 bat.2 or both and off.i now have only one battery which is a deep cycle but from what i read here you guys say deep cycles should really not be used to turn engine on.so im going fishing tomorrow night so i want to instal a cranck battery.so this way i put my switch on bat.2 cranck and run engine with that one and when im fishing switch it to bat.1 the deep cycle one for my livewell and lights and other goodie.so all i have to do with new battery is positive to switch and negative to the negative of the deep cycle right

bowman316 · Apr 30, 2009

Re: where does my negative go on dual battery

hook your motor negative up the the starting battery, and positive up to comm on switch. I don't think it matters which negative you hook it up to, but just hook it up the the starting batt.

you can hook up the troling motor directly to the deep cycle, or hook the positive up the the switch, but the other way doesn't make you turn the switch all the time.

Vic.S · Apr 30, 2009

Re: where does my negative go on dual battery

Ah you didn't say anything about the change over switch in your original question.

Yes connect negative from engine to starter battery, negative of deep cycle battery to that.

connect the positive of one to connection 1 on the switch (suggest that is the starter battery but not important so long as you know which is which).
Connect the +ve of the other to connection 2
Connect the engine positive and all your other stuff to the "common " connection.

When the engine is running do not switch to OFF you could blow the diodes in your rectifier. Switch from one to BOTH then to the other.

When the engine is not running it's not important but normal practice is switch between batteries via the OFF position

bowman316 · Apr 30, 2009

Re: where does my negative go on dual battery

and you don't have to run every positive wire off the common connection, you can still run wires off the deep cycle like before, if you only want those accessories to use that one battery.
i deep cycle ran out of juice last week, so i started the motor on the starting batt, then switched over to the deep cycle.
it gave me maybe 10 more minutes of fish finder use from the batt.

pitbulll · May 1, 2009

Re: where does my negative go on dual battery

cool tthanks guys for all your help.one more will it make a big difference if the negative that goes to the motor be connected to the deep cycle cause if i try to disconect it and conect it to the starter batt. i would have to buy a long cable to reach it

bowman316 · May 1, 2009

Re: where does my negative go on dual battery

yea, just connect it to either negative terminal

pitbulll · May 1, 2009

Re: where does my negative go on dual battery

thanks bowman

where does my negative go on dual battery

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