Batteries

Not sure about a Quicksilver battery, but an 8D should give you about 3 days on a 12v fridge (unless the kids are leaving the door open).

Deep cycle/golf cart batts are your friend, invest in one bloody good one and you should be fine. Make sure the charger is set-up for wet batts, not gels. You can't mix'em.

I had the same model Carver and installed 4 Trojan golf cart batteries to run my house system. I also installed a 3000 watt inverter with a 100 amp charger. I put two batteries back against the wall to the aft cabin and two just beside the transmissions . I also used two deep cycle batteries for starting engines and genset.

How about running the generator enough to keep up with the load demand on the battery?

Not a Carver, but I used two 75 satt solar panels to charge 4 golf cart batteries which ran a "Cool Blue" fridge and freezer system. With sunny weather I could sit for anchor indefinetly without starting the main engine to charge the batteries.
-18 C in the freezer and hard ice cream in the Exumas, life is good...(cold beer was also included)

Find out what the daily load on your fridge is? (Amp hours)
Then you will know what kind of battery you need and how often to charge it.
Also keep in mind to never discharge a deep cycle battery below 50% capacity, it will shorten it's life considerably.
(I used 70% as my target, the bank lasted 6 years)

Keeping the batteries in the engine compartment is probably not a good idea,

Heat and vibration.
The recommended location is in a clean, cool and dry.

Are you saying that 8D dies after 36 hours and you haven't re-charged during that period? While you're not on shorepower, yes?

Many 8Ds will give you about 245 amp-hours, discharging to 50% means 120-ish available before recharging... so how many amps does that fridge need? Is the fridge running on DC, or is it running on AC from an inverter? What else is running off that battery, if anything?

Are you drawing that battery down to near zero state-of-charge? Anything below 12.0V? How often do you recharge?

FWIW, we have 300 Ah banks (150-ish usable) with a relatively economical fridge on each, and I have to recharge 2x/day.

I've read most 8Ds are not deep cycle batteries, even when the label says it is. Dunno anything about yours, but that's one of the reason some folks choose golf cart batteries, which are said to be true deep cycle. Four of those would give you more like 440 Ah at 12V, and might easily fit.

-Chris

are you saying your 8D will run your fridge for 36 hours and then die?
that is a long time.
I have an 8D house battery and only use the inverter when I turn off the generator over night for a few hours.
Depending on how cold the fridge is and how many AC lights I leave on there is usually enough juice in the 8D until I start the genny in the morning.

BTW, here is a trick I learned to get more out of the battery:
I turn the fridge all the way up and leave it on high.
The fridge use a lot of juice cycling the compressor on than it does running constantly.
I have a regular AC fridge, I don't know much about the AC/DC fridges.
I shut the cockpit freezer and usually leave the ice maker on.

Which model NovaKool? And in what kind of exterior/interior ambient temps? Three days if outside and inside temps are in the 60s is likely different than if outside temps are in the 90s and inside temps are in the 80s.

Ours are both NovaKool, but I've never tried to run then for days without recharging. And we have other loads on the batteries, too...

As to alternatives, GCs would probably be good, but why not just recharge more often?

-Chris

NovaKool amp draw chart. Note values are based on 75-degree temps, after the unit has reached desired internal temps.

http://www.novakool.com/documents/ampdrawperunit_001.pdf

A bigger unit -- e.g., RFU9009 -- would draw 234 amps in a 36-hour period. That'll kill an 8D...

Even smaller units that draw 4.4 amps would be using ~158 amps in a 36-hour period, drawing an 8D down to about 35% SOC.

-Chris

Why not just get a Honda 2k portable generator and a big battery charger and just run the generator for 3-5 hours every couple of days and charge the battery?

I don't see an RFU 9000 on that link, but I'd guess then maybe their RFU 9009 draws about the same amount of current. (Your manual will say.)

If it's 6.5, and the 8D provides around 245 Ah, the math says you'll reach 50% SOC (122.5 Ah) at about 19 hours.

For comparison, 4x GC2 golf cart batteries (slightly larger footprint than one 8D, not as large as two 8Ds) would give you about 440 Ah, and about 220 Ah to 50% SOC, at about 34 hours.

I don't necessarily see "three days" anywhere in there, although that can be influenced by ambient temperatures and your climate may be an example of that.

There might be some Lithium (LiFePO4) solutions, but at serious expense and apparently with a learning curve. But maybe solar is more mainstream, assuming you have the real estate (and the wallet).

-Chris

He might not have enough sunlight up there to make solar a viable option. If you're anchored, I don't see why a little portable generator cannot be run for a few hours everyday with a large battery charger, or just start the main engine and run it a little while.