I would use a dedicated starting battery. Biggest reason if your troller depletes yôur juice, you're f'd. Not sure what kind of motor you have, but I know with my old Opti it was recomended to put the battery as close to the motor as possible, and have a battery that was HOT. Most starting batteries are specified as such because they have higher cranking amps.

I'm sure it would work, but that's not how Id run things.

 

X2 and then your big motors charging and ignition system is dedicated also to that battery

 

Funny you say that. Few weeks ago ran batteries too low cuz I was thick into fish and had to pull Start her lol

 

I have my batteries hooked up exactly like your describing, I've had no issues so far. BUT, keep in mind I run my Generator and Convertors virtually all the time so my batteries never discharge.

 

would starting my outboard like these draw a lot of power from my batteries?

 

What size and model outboard? how many cranking amps does it require to get it going?

 

It's a 1988 johnson 35hp. Not sure on the cranking Amps just curious if starting it a few times on a trip is having a big impact on my batteries

 

Low voltage on your start batt. is hard on the starter.

 

I just finished up wiring a troller, 75# Motorguide 24v. The only attachment I made to the cranking battery was the negative terminal of the trollers to the cranking battery negative and that is for a little piece of mind to lessen any chance of electrolysis. I thought like you did about tapping the cranking battery. It would work but like was mentioned you'll be pull starting if it runs down. Deep cycle batteries are made for the drain.