# Max distance between battery and outboard?



## Gatorgrizz27 (Apr 4, 2015)

I’m building a skiff with a 12v bow-mounted trolling motor, and 20 hp 4- stroke or 25 hp 2-stroke outboard with electric and pull start. I REALLY only want one battery, mounted in the bow. I also have a mount to move the trolling motor to the stern, so I will need to run 15’ of at least 6 AWG wire back to the fuse block regardless. 

However, I’m worried that I may not be able to crank my outboard with the battery 15’ away, even if I bump the wire size up to 2 AWG. The outboards recommend at least a 400 cca battery, but I can’t imagine they actually draw 400 A when cranking. Minn Kota’s chart shows that 2 AWG is suitable for up to 116 A with a 15’ run, and that is constant use with a trolling motor, not cranking an outboard for 10 seconds. 

I’ll add a small cranking battery if I absolutely have to, but I’d much rather only have one. Trying to keep this boat light and simple.


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## firecat1981 (Nov 27, 2007)

I think you'll be fine. If memory serves I have a 4ga ran 10ft to my 20hp and TnT. You won't be using the outboard and TM at the same time.


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## Smackdaddy53 (Dec 31, 2012)

There’s a chart somewhere with voltage, gauge and distance.


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## Gatorgrizz27 (Apr 4, 2015)

Thanks for the replies. I’ve seen the marine charts, but I don’t know how many amps the starter draws, which is the problem. It’s also a momentary load so it’s not the same as a trolling motor or bilge pump, which means smaller wire should suffice. The thing that gets me is that the leads on the outboard itself are relatively long and look to only be about 10 AWG. Obviously I would cut those as short as possible coming off the fuse block.


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## Vertigo (Jun 3, 2012)

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

100 to 150 amps for an outboard starter, closer to 100 for 20 hp.


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## anytide (Jul 30, 2009)

closer the better. 
big wire goes far, but your losing it down the line. 
tough on starters and battery life.


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## Gatorgrizz27 (Apr 4, 2015)

Thanks for the info. It looks like with 4 AWG I’d be at a 3% drop over 15’, assuming the starter draws 100 A when cranking. The trolling motor will be fine with 6 AWG, even when running in the back of the boat, the majority of the time it will be run right next to the battery. 4 AWG should give me enough reserves to power the other stuff that will be on in the boat, even with the trolling motor running. 

I’d be more concerned with the voltage drop to the outboard if it was a newer unit with fuel injection, ECU’s etc. For a late 90’s carbed 2-stroke, as long as the starter is spinning quickly enough, I’m sure it will fire up fine.


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## not2shabby (Sep 14, 2016)

I agree. I think you'll be just fine with 4awg. The cost difference from www.TinnedMarineWire.com is almost exactly $1/ft between 4awg and 2awg. For pos & neg, you'd be looking at $30 extra to go to 2awg. Not bad, in my opinion, if you want that little bit of extra insurance.


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