[boatpoker]

Short answer, yes your batteries will run down at some point if not on shore power.
Real answer, needs a lot more info as Don L said.

 

[boatpoker]

Except if

It is all just simple math. If your fridge operates at 3 amps an hour, and you have 300 amps of battery power, you will need to charge every 100 hours. Solar helps, but unless you have a pretty decent array, you may not keep up with the consumption. As I said, simple math.

Except if you take300amps of a 300amp/hour battery ... it's dead and will likely never likely recover.

 

[boatpoker]

Sorry to jump in here, not trying to derail or hijack the thread.

but is there device to measure how much juice a specific instrument uses over a period of time. IE could I wire up a bilge pump counter or an hour meter to it such that each time the unit cycles on and off I can figure out my usage?

if a refer used 3ah, thats great, but we know that its generally not running continuously it is cycling on and off. so its actual consumption over the course of 24 hours isn't likely 3 ah..Right?

in my situation, Ive got two banks set up and each bank is 2 6v gc2 bats (capacity 215AH 110 min reserve cap @ 75 amps) wired in series to get my 12v.

in theory, if my refer drew 3ah continuously.
i could run for 71 hours and kill one bank beyond recovery. or 35 hours to only use 1/2 of my available capacity. or 57 hours if I'm feeling lucky and want to go down to 80% cap Right? assuming no other loads on the battery...

Google "Battery monitor"

 

[boatpoker]

you're 12 volt refrigeration system won't kill your batteries unless you want it to, they are very very low horsepower can't even measure it in horsepower so it's measured in amps or Watt hours. The refrigeration effect is very small which is why they're usually applied to very small boxes.

Basically, All 12/24 volt refrigeration systems are a modern miracle which came along inearly or mid 80s!

Just for fun I ran my new unit on a single battery for 2 days and the battery was still able to start the engine of the boat,

Most 12/24 volt refrigeration only draws less than five amps (you figure out your amp hours because everybody's boat is different).

Nobody does it of course unless they're full-time on their boat but, once the box is cold, it tends to stay cold with less energy then it takes to run the system from a "hot" start.

I think you missed a few things Denise. The OP knows nothing about amps vs. amp hours, voltage, how to measure the the condition of his batteries or even the conditioo or type of his batteries or whatever else he runs on 12 volts. I believe he also said he has 2" of crumbling old insulation.
I believe you are being a little optimistic.