I have a pretty much brand new 2023 Alumacraft Competitor 205.  It was a dealer show boat so it has 12 hours on it.  I took it out last month for a shakedown cruise and everything worked great.  Today, I pulled up at the boat ramp and it's D E A D.  Nothing.  No beep on key turn.  No tilt trim at the motor itself.  No accessories lighting up.  Not even the horn, which I think has to be hard wired. 

 

It has a MinnKota 3 bank smart charger.  The installed charger shows all three banks @ 100%.  There are two batteries in the rear for crank and power steering pump and a 3 battery 36v system under the floor for the accessories.  

 

I've checked cranking batteries:

Connections are tight

Fuses are intact 

Master power is on

Kill switch is properly set

Putting a jump block on the cranking batteries had no effect.

Key in different positions 

 

What am I missing?  With how dead everything is, it has to be a short somewhere I think.  I'm going to get my voltmeter, but I would LOVE it if it was something I was doing wrong.  

 

The 36 volt three batteries pack under the floor should be for the trolling motor only.  You have a three bank charger and 5 batteries.   Could the 3 bank charger be for the trolling motor batteries only?  That would explain why the charger shows 100% and everything else is dead.

 

I would start by checking the status of the two batteries in the photo that are wired in parallel.  If they are dead then you found the problem.

Is there a power shut off anywhere?

I think one of the cranking batteries is kaput. But, I'm not used to 2 battery systems so if someone would educate me, I'd appreciate it.  I read 27v using the closest battery as my negative and 0v when using the other battery.  My confusion is how I can read 27v if one cell is dead.  Wouldn't it be closer to 12?

I can't tell for sure how the batteries are wired in the photo but every indication is they are wired in parallel.  If so they function together as a single 12 volt battery with double the capacity.  The way to check each battery is to remove all wires and check the voltage across the two terminals.  If you get a low voltage then you've found the problem.  The best way to test them is with a battery tester.  Any auto parts store should test them for you for free.  You can buy a battery tester for around $25.