I posted a review on my initial impression of the Dometic CFX-40W about a year ago. Those who are just starting their research on this topic can find my unboxing and initial impressions here.
Over a year later, I remain pleased with the purchase. I would still pick the CFX-40W over the 35 because I prefer to have the additional refrigerator volume (yes, I have filled the unit to capacity more than once). The CFX-40W also works great as an arm rest for the second row passengers without any additional cushioning.
Regarding power, to ensure that the unit stays powered on at night and other times when the Model X is off, I purchased a small sealed 12 V battery which I use the Model X to keep charged and then I run the Dometic off this battery. All of this fits easily hidden away and securely in the "under trunk" space in the back of the X. I decided to do this after monitoring how quickly the internal Dometic temperature rises on a hot summer days when the power is removed. This setup has kept my Dometic running continuously (except when it's removed for cleaning) for over a year now.
You may find the following links useful if you are interested in exploring such a setup.
ExpertPower EXP12180 18Ah 12V DC battery
Attwood Small Battery Box (vented) for above
I also use a small DC battery charger controller that was originally intended to charge battery banks off a solar panel source to keep my dedicated Dometic battery charged. I like to think this setup provides extra protection for the X's internal 12 V battery, but I don't think it's actually necessary. But, if you do implement this option, be sure to use a fused accessory socket such as these:
CUZEC Heavy Duty 15A Male Plug Adapter (Fused)
NOCO GC018 12V Adapter
Disclaimer: Please be careful! Although the voltage isn't high, an 18Ah 12V DC battery can deliver more than enough current to shock and even seriously injure you if you are not careful. If you do not understand basic electronic concepts, find someone who does to help you. You have been warned! Although this has worked well for me, I assume no responsibility or liability for your actions!
Ha! Talk about perfect timing! I’ve followed your thread from the inception and finally bit the bullet on getting the 40W model. I was wondering the exact same thing regarding extended down time and what happens to the internal temps when not powered.
Question, how long did the the temp stay “cool” enough before warranting a battery backup? I know that’s relative but maybe under 45-50 degrees before I’d start to worry?