Trying to figure out how many batteries I should have onboard for a full day fishing trip. I have a 21 foot boat and will be using a 36 volt trolling motor. There will be two graphs on the boat. Do people normally run everything off of the three trolling motor batteries? Or is there typically a battery designated for the electronics? Thanks, Josh

 

In your case, 4 is the norm.  Trolling motor batteries are usually dedicated to the TM only and the cranking battery handles everything else.

ALWAYS  have a dedicated cranking battery!

all accessories, lights, and pumps are also connected to the cranking battery.  

 

so you need 4 batteries....... 3 for trolling motor and 1 cranker

 

Thanks for the responses. I always have a battery dedicated to cranking. Should've been more specific with my info. Just didn't know if the electronics would be too much for the cranking battery to handle. 

 

Install a 4 bank charger. That way you're positive the cranking battery is charged 100% every time. I know some of the walleye guys are using 5, having 2 batteries in parallel for cranking. More so for insurance. Not wanting to get stuck out on big water not being able to get the big motor started. I carry a jump box for insurance and someone also makes a switch you can use the trolling motor batteries to jump the starting battery if it went dead

 

Good idea on the 4 bank charger. I appreciate the advice.

 

4 banks are great however if you don't want to spend the extra and you don't fish tournaments, you can get away with a 3 and install a toggle switch on one of the bank leads so you can switch which battery is charging. If you do fish tournaments though just get the 4 instead because it's tougher to get all 4 charged before the next day. 

is it possible to run electronics such as fish finders off a battery such as a drakon(with direct power toggle switch) and then the engine to a cranking battery while having two separate batteries for a tm? 

You may need a good cranker depending on your outboard and electronics. I had to got with the Sears 1150 cca agm to keep up the voltage so my units would not shut down at startup with my Optimax. I run 2 Low hds units with a 225 Opti. It takes a lot of juice to make it with adequate voltage running a livewell pump and my units.