Battery/12v Fridge Help!

Not sure if this is the best place to post this - but I’m running out of ideas.

Purchased a Genesis Off-road dual battery kit along w/ their “G Screen” (battery monitoring) about 2yrs ago to pair up w/ an ARB Zero fridge/freezer. I remember the 1st run being awesome - dry ran the fridge for several days in the driveway without starting the rig at all. Now when we’re out off-grid, I have to start the truck at least twice a day to keep up with the battery consumption to keep it from dipping below 12.2v - & the battery monitoring generally has either battery resting at 12.5v or 12.4v rather than where I would assume a healthy battery would rest (12.8v) after just 10-15min after shutting the truck off.

I’ve tested both batteries (pics of results after it sat for a couple hours) & both show good health (2 x Odeyssey ODX-AGM34)

I pulled off all aftermarket accessories that I’ve installed over the years off of the positive battery terminal today to see if that kept the voltage from falling after engine cutoff, but no dice, so I don’t believe any of those items are an issue.

I also replaced the alternator already w/ a HO unit from DC Power just in case that might’ve been the issue - that & it was still on the 16yr old OEM - charging doesn’t appear to be any issue.

From all of the forums I’ve read & posts on here it seems the consensus is that you should expect for a 12v fridge to run for at least a couple of days if you’re using a dual battery setup - but I am just not seeing anywhere near that kind of life out of it - it’s made the last few mountain treks a bit annoying to have to keep checking battery health.

Anyone have any ideas?? I’m not the sharpest when it comes to tracking these kinds of issues down, but I’m willing to try anything.

Appreciate y’all’s help & time.

 

not really sure what could be wrong but if it was me, I'd take out the dual battery kit and just run a single battery and see how long the fridge can run. Alternatively, take out one of the batteries, makes sure its fully charged, and connect the fridge directly into it. see how long it runs. Essentially, take the dual battery kit/system out of the loop and see how the battery performs by itself

wonder if the dual battery kit has something to do with it.

 

I had thought about doing that. Issue w/ removing it completely is of course I was an idiot & tossed the OEM battery setup when I put this in back in 2022. Now I don’t have the hold down or the tray. But I could rig something up temporarily just to test.

 

just take out the secondary battery and leave it hooked up at the house to test it out. actually i dont know how your system is setup but i guess that may not work if you have to daily drive the truck

 

Yes, I’ll do this tomorrow & see how it goes. I’d be super bummed if it ends up being Genesis’ unit, but perhaps they’d work with me on it. Thanks for the suggestion.

 

Have you checked to see what the fridge is consuming power-wise? If you haven't verified that aspect you should, could be something as simple as a poor connection somewhere in the fridge's power circuit.

 

How could I go about doing that?

 

You can put a clamp on amp meter on the power line going to the fridge. You already know the amp hour of your batteries, knowing the current draw and source voltage provides enough info to estimate your power consumption in watts and should help you estimate your fridge duration with real numbers. At this point you really don't know what the cause is, it'd be nice to eliminate the fridge and it wiring as potential culprits. HF sells a small clamp on amp meter/DVM for about $20, I compared it's readings to a Fluke meter and it's easily accurate enough for this. I keep one in the truck

 

Clamp meter gotcha.
I had thought about this earlier & brought the fridge into the house to cool it to temp so I could see the true power draw, but wasn’t sure how to get a reading off the cord. Thanks for the suggestion, I’ll try this as well.

 

Most 12V fridges use around 60~80 watts when they kick on. An advantage of using an amp meter is you are also measuring the current draw cause by any wiring going to the fridge, the wiring and it's connections can have a significant impact on the usage. Since it used to last much longer then the wiring size probably isn't the issue.

According to AI;
"The power consumption of an ARB 12V fridge depends on the model and how often the compressor needs to run to maintain the set temperature:

• ARB Fridge Freezer 50: One review found that this model can use 64.3 watts.
  
  
• ARB Elements fridge: This model uses an average of 0.89 amps/hr when used as a fridge.
  
  
• ARB 10801352 Portable Fridge Freezer: This model uses an average of 0.85 amps/hr at a cabinet temperature of 37.4˚F and an ambient temperature range of 78.8˚F–87.8˚F.
  
  
• ARB 47L Portable Series II Fridge Freezer: This model has a current draw of 0.87 amps/hr.
  
  
• 47 Quart Zero Single Zone Fridge Freezer 10802442: This model can draw under 1.5A during optimal conditions.
  

The amp draw can be affected by the ambient temperature, how often the fridge door is opened, and the contents of the fridge. For example, on a hot day, the compressor will run more, resulting in a higher current draw.

In general, a 12V refrigerator needs 40–80 watts to run, and can be powered by a 100-watt solar panel connected to a battery or portable power station."



You know you're running approx 12V so in any calculations you make can use the measured battery voltage you're seeing. Some specs will be in watts, aka "P". Some values and or specs will be in amps, aka "I". With the above formulas, current readings and battery voltage you can calculate the usage when it cycles on. Since the frequency of it's cycles will depend on temps and how often you open the fridge an instantaneous (clamp on) measurement won't work to estimate how much it needs over time. It will tell you if the fridge circuit is drawing more then it should based on the manufacturers specs. You may need to convert your current readings to watts for comparison to a spec but that easy using the chart above.
I needed to estimate my fridge's consumption. For that I used a power bank and ran it overnight. Since it was 500W every percentage of charge equalled 5W, so if I use 50% overnight I knew it consumed 250W. And since I know the voltage I could calculate the current (amps) it uses over that period of time. That gives me an amps per hour consumption value and in your case that can compare directly with your battery's amp hour rating for estimates.

 

So at your own readings, your batteries are at 75 and 80% charge. Assuming a deep cycle can drop down to about 50% without damage, you're almost 50% down on usable capacity already. A lot of AGM/Deep cycle batteries need more voltage than our smart alternators put out. You said you put in a new alternator, but if it's a smart one it very well could still be putting out what the ECU wants, which is less than needed to fully charge the batteries to 100%. I put in a voltage booster for this exact reason, and it made a drastic difference in my resting voltage/capacity.

Have you tried hooking up your batteries to a battery charger to try and get those %'s back up to 100%?

Might not be your issue, but worth thinking about.

 

This is a great post. I would add to this just a but of my personal experience. I have the Dometic cfx. Initially it did run at or around 50 watts when it cycled on. But after a couple of years, under heavily load it can go up to around 110 watts. If it's really hot out without a breeze it can easy "run" at an average of 80 watts... these coolers lose effective cooling over time.

Another thing to remember. Absolutely never ever put warm things into your pre chilled cooler. They are not effective at "cooling" a warm 12 pack of IPA... they are effective at keeping cold IPA ice cold....

You Absolutely must add a 150 to 250 watt solar system. With it you will generate more power then you can bank.

 

How old is your CFX? My CFX75DZW was mounted in my truck bed under a shell for nearly 3 years, then in my camper for the last 3. Mine is still chugging away in the 63-67 watt range. Have you checked or replaced your cord? They are notorious for failing. They can trip breakers, stop working altogether, or even heat up/melt at the screw together connector. A lot of the Scout Camper owners have had this occur. Sometimes Dometic will send you a new cord, or you can just buy one on Amazon for pretty cheap. I've been lucky though, it seems. I'm still on my original cord.

 

Lead acid batteries are really not a good option for what you are doing, That they are AGM helps, but only so much. Lead acid batteries excel at dumping big current over short periods, you are after something that is made for dumping little current over a long time. Further, lead acid batteries incur damage when operated below 50% capacity, so just not ideal. If you can swing it, a LiFePO4 battery would suit your application better. Don't know what fridge you have, but assume 60W, or 5 amps to operate. A 100 amp-hr battery at 30% duty cycle would last ~60 hrs between charges.

 

@PlinyTheDawg , do you have any friends with a power station you could borrow? this would be a super easy way to test your fridge's usage.

And like @G2.M6 said, it's extremely important that everything is pre-chilled. They really do suck power having to cool stuff off from ambiant. I recently set my ARB (an older model) to 0 degrees F in my garage (which was admittedly like 80+ degrees) and filled it with that temperature of powerades and a carton of ice cream... the ice cream melted, and it took running for 18+ hours to get stuff starting to freeze. Was over 24 til everything was froze solid, and that was running pretty much 100% and plugged into 110v at home. I emptied my 500wh power station daily keeping that thing frozen, and that was with a 100w solar panel (in 100 degree weather).

 

Good idea - my buddy has a Goal Zero. I’ll see about borrowing that to run some tests.

Yes; everything that goes in the fridge is pre-chilled, & we always cool the fridge down to temp at least a day before so it’s not boosting to chill from the battery.

 

OK that battery meter that is telling you the battery is "good" is not testing the battery under load. My guess is that after two years one or both of those batteries have become degraded. Take it to a place that can do a batter load test on the battery like autozone or batteries+. AGMs are not good at being drawn down more than 50% and if you have done that consistently for two years, those batteries may not be able to hack it anymore.

 

Interesting. The Odyssey's were the battery’s suggested by Genesis, I was thinking they would be ideal & long life using for powering a fridge off-grid for several days.
I’ll add taking it by Auto Zone for a load test to the ‘to do’ list before I take the battery assembly apart to do a single battery test minus the Genesis battery combiner.

 

Those batteries should be fine. I had two optimas that only had 4ah more each, and I seldom had any issue running my fridge for a 3 day weekend. A battery could be bad, but in general, that should be enough for a weekend, AH capacity-wise (assuming the fridge isn't sitting in 100+ temperatures).

 

Windows are usually down for the truck to have some airflow, don’t think we’ve ever been out in 100 degree temps with it, but definitely in the mid to high 80’s..
Generally the batteries separate themselves, but you can manually tie them together in series - I would definitely think especially when tied together that both batteries should be able to tank through it no problem for a couple of days. But we’re talking hours at this point - it’s embarrassing.