Dual Batteries, Negative Cable layout

evantful

Petty Officer 3rd Class
Joined
May 11, 2014
Messages
90
Hey all quick question. Im adding in a second starting battery on my 20ft Cobalt. It currently has a On/Off Perko switch, so I will be swapping that out with the Dual Battery Perko. I don't want to add an ACR or anything beyond that as I won't be running any "deep cycle" loads. I simply plan on alternating batteries each day out and just wanted the added security of a second battery as I do 30-40 one way mile runs up and down the Hudson River.

I just had a question in regards to the Negative Battery Cable layout. Should I run the negative cable between the two batteries and then to the engine block, or two separate negatives to the block?
What are the differences?
 

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gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
eventful, that fact that you will use one battery at any one time, I would say go with a ground wire between the two batteries. You would not gain anything by running separate grounds from each battery to the engine case. So save the wire, money and time and share the grounds and happy boating... JMHO!
 

lmuss53

Lieutenant Junior Grade
Joined
Sep 9, 2008
Messages
1,227
I agree with the above, I am running a Perko switch in my Sea Nymph, second battery sits right next to the original with a heavy bridge wire from neg to neg on the batteries, this setup has worked fine for several years.
 
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StingrayMike

Petty Officer 1st Class
Joined
Aug 17, 2014
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355
I agree with gm280. Seperate ground wires really dont do anything, a ground is a ground. It all ends up at the block anyways.
 

evantful

Petty Officer 3rd Class
Joined
May 11, 2014
Messages
90
Ok thanks everyone!
Currently the boat has 1 Gauge Marine wire going from the battery to the switch, engine ground, switch, and from switch to alternator. No length is over 5ft.
Will 1 gauge be a heavy enough bridge from one battery to the other (about a 2ft length)? And is ok if I bridge them using the secondary threaded stud (not the clamped top terminal) on the battery before the engine ?
 
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lmuss53

Lieutenant Junior Grade
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Sep 9, 2008
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1,227
Same size wire is fine and as long as you go from grd to grd either terminal is fine.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
There is an advantage to running a separate ground to the same point on the block as the other battery. Electrically either method works but should a problem develop in the cable between the block and the battery it is attached to, you lose the second battery power as well. A separate ground eliminates this problem except in the instance where the bolt securing both cables to the block comes undone.
 
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