this post was submitted on 18 Mar 2024
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A little more technical, I don't think your average starting battery is 100ah capacity, and most don't rate themselves in amp hours either.
I bought a deep cycle for my little sailboat at the local auto store and it's around 70-80ah
You would need an inverter to convert the batteries DC (direct current) into AC (alternating current). This will "cost" some power (watts) to convert that voltage. Your refrigerator runs on AC battery outputs DC.
That said, it is quite common to run refrigerators on larger boats and RVs off batteries and it would certainly be possible to run your house fridge off a single car battery for a short while if you've got an inverter large enough to run it.
What your not gonna do is just run out to the car, grab your battery and hook it directly to your fridge.
Our fridge uses between 130-180 watts when running and about 2.9Kw or 2900 watts in 24 hours. Your battery most likely has under 1000 total watt hours til empty, and car batteries are generally not used past 50% capacity (lead acid starting battery). So figure 500 watt hours max (for easy math). So... 4h run time maybe.
In your last paragraph, most of the places you write watts you mean watt hours. Good reminder that Wh is a bad unit, since it's too easy to confuse with watts.
Good catch... It was early and I was on my phone (my excuses) :)
It's just the 2.9kw should be kWh. Everything else is close enough.
While it's true that it won't be at max capacity, I will say that batteries these days will rate themselves in amp hours. For instance usually an 800 CCA AGM battery lists itself online as 7.5 AH.
The conversion process involves using the formula CCA = 7.2 x Ah to convert from Ah to CCA, and Ah = CCA / 7.2 to convert from CCA to Ah.
I specifically looked at the available specs at the local auto parts stores and couldn't find Ah details. This was about 2y ago, so maybe this value is becoming more commonplace. I know in the RV/Sailing works Ah is used pretty exclusively. My deep cycle AGM only lists CCA and reserve capacity
With the rise in power banks and phones being rated in Amp Hours, I think this may be a recent change, and certainly one I have noticed.