I run my electronics off a second battery because cranking the engine was dropping the voltage on my electronics and causing problems. My set up is very different that most, I have a 36V trolling motor and only three batteries on the boat to save weight. One of the three is used to crank the engine, one for depth finders and NMEA network and one for the stereo, bilge, lights, etc. The trolling motor pulls off of all three.

 

i have 2 batteries as well and i run very minimal electronics i run the motor off the same battery as the depth finder and use the second one as you do ( back up ) my radio plays in my head LOL or we use a bluetooth speaker to the phone or IPAD.

 

I added a 2nd battery that I run my stereo, GPS, pp, JP and all accessories separate from the cranking battery. I installed the blue seas add a battery with perko switch. This charges the cranking battery while running and it senses the voltage and switches over to the accessory battery once the cranking is full. This setup also works good with the on board charger when it's in storage as it charges both batteries using just one leg of the charger.

 

I have two only batteries. One is to crank and for my two Lowrance GPS/NMEA 2000. The other is for lights and everything else.

Then I have those two for my 24v trolling motor.

So i have 2 batteries with three seperate isolated circuits. two 12 volt circuits and one 24 volt circuit.

Be careful how you wire it or you will burn up the motor electronics.

Also the NMEA 2000 has a shared ground through the motor. I couldnt tell if it was isolated or not so i run the same starting battery also runs my NMEA 2000 and the two GPS hooked up to it. Didnt want any chance of back feeding as that second ground does carry 24 volts.

2 lithium smart batteries up front under front deck for the entire boat. nice and light. the second battery not charged by the outboard will be the limiting factor. When the trolling motor dies due to that battery dying out then i should have plenty in my first battery to start outboard and go. fail safe. (hopefully)

 

I have 2 sealed lead acid batteries and a Blue Seas Add-a-Battery system on my boat. https://www.bluesea.com/products/7649/Mini_Add-A-Battery_Kit_-_65A One battery is strictly for the TM and the other battery is for engine cranking, radio, and GPS. I prefer to use Interstate dual purpose marine batteries and ensure that both have a high Reserve Capacity Ahr rating. http://www.interstatebatteries.com/content/product_info/marine_f.asp
This set-up hasn’t failed me in the 11 years I've had my boat and I do replace the batteries every three years just be sure.

 

I do

I have two batteries. One for all electric and one to start. Two battery switches. I set one to 1 and the other to 2. Both batteries are wired to both switches. For setting 1 I use 12 gauges wire for electronics. Setting 2 both switch are set with heavy battery cable marine wire. If needed I set both to 2 to start the motor. If needed I can set the starting battery to run electronics.
This is a very short explanation of how I wired it. I made all the wiring and set this up myself. But I love this setup.

I have an on board charger for the electronics battery. The motor charges the starting battery. The batteries are identical. Both are in my console. Boat is a 20 whaler I restored.
Archie

 

I use blue sea

 

Two batteries, regular in the rear for essentials (motor crank, GPS, VHF, and nav lights), and a big deep cycle in the center console for fishfinder, stereo, courtesy lights. When the boat is in the garage, the deep cycle is hooked to a trickle charge/floater. The crank battery ALWAYS gets checked and topped off the night before leaving. I figure I can live without tunes and fishfinder as long as I can get home, and if the crank battery dies at sea, I can use my jumper cables (always in the boat) to start the motor and make it home. When I add my trolling motor, I'll add a pair of deep cycles just forward of the other deep cycle in the center console that will be purely for the TM.

 

Yup, blue seas add a battery with the scr. Best set up IMO and we sell and install lots of them. All the advantages as well as it only needs a single bank charger to charge both.

www.g-spotservices.com

 

I think i'll research this Blue Sea System. Either that, or the description from ACassidy seemed pretty good as well.

Thank you guys for the ideas.

 

I'll be using two batteries as well, probably dual purpose marine, group 27. One in the rear sponson, will be for cranking the motor and a jack plate. It will recharge from the motor. Another, under the console, for lights and electronics. It will recharge from an external battery charger when I am dockside. My question: should I tie the two grounds together? I won't be using Perko switches as there is no need. Each system will be independent, but will tieing the two grounds together prevent any weird arcing, sparking and such?