the question I have, Do I need to have both a cranking and a deep cycle (house) battery on the boat? Or would a single group 27 dual purpose battery be sufficient power source for my electrical needs? (Forgive me if this is a dumb question..)
The outboard will charge the battery while underway. On your list, GPS, jack plate, trim tabs and likely live well pump will all be used concurrently.
That said, most skiffs have a single starting battery that also serves as a house battery for accessories. A trolling motor battery is wired for separate operation but many are rigged on multiple bank chargers.
You will be good with one. The jackplate and trim tabs are mainly used while running. Nav lights are probably LED so don’t drain any power. The GPS uses very little power.
Keep a jump pack on you just in case - that’s always smart no matter the setup.
You could run the accessory wires separately and use a smaller lithium for them, but that’s only if you run into issues down the rod for some reason. That would save space and weight instead of getting another lead acid.
my setup is like yours but also one power pole. no issues unless i fish using power pole heavily for 3 hours. then i make a run or double check noco charge.
Get a dual purpose cranking/house battery that has enough CCA (cold cranking amps) and Ah (amp hours) to start your engine and run your accessories (get the battery with enough Ah to operate whichever accessory draws the most amps for the length of time it will be used without running the engine which will charge the battery. I operate my jack plate and trim tabs at the same time right after shutting down to start poling an area and the chartplotter is on at the same time so add those up. I bet @iMacattack would know more than me for sure but this is what I’d do and it might not align with what he recommends. I like to have more battery than I need just to be safe!
A good rule of thumb is to get a battery with more Ah than what you calculate you need. Maybe 20% or more. Be sure to start with engine manufacturers recommended Ah and add the other accessories. An under rated Ah battery can still crank a motor for a while, but will die quickly as it gets older due to the load it is constantly working.
Lead Acid batteries can typically fail without warning…. It just wont crank at one time. A steep fall off in Ah. (ever have a car just not crank one day when it seemed fine the day before? And a new battery fixed it)
An AGM battery typically does not have the steep drop off in life like the lead acid, so you may observe it getting weaker before it dies. Also, AGM batteries are more vibration resistant, and spill resistant, which is better in our applications.
Modern chargers like the Noco are very sophisticated. Putting any battery on a quality charger regularly, like a Noco, will make it last longer due to its “conditioning” of the battery. You can not harm a battery with these modern chargers leaving them on 24/7 for extended periods.
An option you may consider:
I plan on adding a Lithium house battery one day and run my accessories off it: GPS, live well, accessory lights, cell charger, power pole. Because its Lithium, it can be smaller, lighter with less Ah because you can draw a Lithium down almost 90% or so without damage. Lead acid and AGM deep cycle or dual purpose batteries can only draw down approximately 50% of their rated amperage before they are damaged.
All “safety” circuits: bilge pump, nav lights will be on the cranking battery that will be charged by the motor regularly.
Just trying to give you some background and thoughts to investigate as you decide how to tackle it.
Good luck.
Lithium’s are normally not authorized for cranking, unless you own a later model Mercury…Yamaha has some specific reserve capacity requirements which is why many use Interstate Lead Acid…currently I have a Merc XS and use a Relion Lithium which was recommended as OEM.
For the Suzuki DF115 outboard motor, a 12-volt cranking-type lead-acid battery is recommended. The minimum requirements include 650 Marine Cranking Amps (MCA) or 512 Cold Cranking Amps (CCA), and 160 Reserve Capacity (RC) minutes, according to Crowley Marine. Dual-purpose (cranking/deep cycle) batteries can be used if they meet these minimum specifications.
You should be able to set your chart plotter to give you an alarm at a desired voltage. I’m not sure what it’s currently set to maybe 11.1 you could bump that up to 11.8 so if your engine is off and you’re using your battery and it’s draining too much. You’ll get an alert hopefully with enough time to still get your engine started.
I would just run one battery and have your jumper kit