Car battery as energy alternative in hurricane?

As a recent immigrant to South Florida, I’ve been worrying about hurricanes in general but specifically about coping when our power goes down for a couple or three or five days, as I hear it tends to do. Specifically, I wonder what use I can make of my car battery for electrical power.

Without knowing a blessed thing about car batteries, I would think they’re an easily accessible power source but I have no idea how to maximize its use. Aside from charging my phone with it, is there a way I could say run a fridge off it for an hour or two? To take that example, say the power goes off. If I leave my fridge closed, the food should stay cool for a few hours, maybe a day, but if I were to power it up for a few hours, that should give me another day. The freezer will go, I understand, but that’s ok, I’ll just eat the frozens once they defrost (probably needs it–I have things in there I haven’t even seen since Hector was a pup.) Has anyone invented a storage battery that works off a car battery that I could use to power up a fridge, or plug into a lamp for some working light in the evenings, stuff like that? Seems like an easy enough product to make, and a useful one, but I’ve never heard of one.

A lot of camping trailers do just this. It is a DC to AC inverter. How useful it is depends on the efficiency and amperage drawer of the fridge and the capacity of the battery.

My BIL uses a few solar panels to charge several truck batteries to power his trailer through a good inverter. The fridge is on the small side and very efficient.

The inverters have been around for a long time and fridges have gotten a lot more efficient over the last 25 years. So all of this is much easier now.

A typical lead-acid car battery is a poor choice for powering things. For that you will want to use a deep-cycle lead-acid battery. But then you’ll need to charge the battery, of course. Either periodically or on a (more-or-less) continuous basis. You can keep the battery “topped off” using a battery charger powered from a wall receptacle in your home. You can also use PV arrays, windmill(s), or a generator. The latter can be powered using gasoline, diesel, or natural gas. A vehicle with its engine running is basically a generator; the alternator can charge the battery. Lots of options, as you can see.

As already mentioned, you’ll need an inverter to convert the DC to AC.

I’ve experimented with using my car battery (with the engine running) to power a fairly large refrigerator. I found that an 800 watt square wave inverter works just fine. A 600 watt unit might also do the trick, but I don’t have one to test. These types of inverters are fairly cheap. If I turn off the engine, the battery will indeed operate the refrigerator, but for only about 30 minutes. The battery is a standard automotive battery, not a deep cycle unit.

Just to add: a modern well-insulated fridge will usually stay cool longer than that, if it’s not opened and it’s reasonably well stocked (i.e.- not mostly empty). We had a three-day outage here some time ago when a windstorm damaged a power substation, and when the power came back on three days later the stuff in the freezer was still frozen and the refrigerator part still fairly cool. It was a while ago and I don’t remember if anything at all in the fridge was spoiled or suspect, but generally pretty much everything was still fine.

I would also add that a specialized lead-acid car-type battery, packaged with an inverter, charger, and various electronics all in one box, is basically what a UPS is (uninterruptible power supply). However the high-capacity ones tend to be costly and even then will have limited runtime when operating full-size refrigerators and the like. If I was anticipating the likelihood of long power outages I’d probably be thinking in terms of a generator.

It must be kept in mind, of course, that the alternator is providing all the power in that scenario. The problem is that a typical alternator is not really designed to provide lots of current on a continuous basis, especially with the engine idling. (With the engine idling, the alternator’s RPM is low, and the airflow through it is low.) Would be O.K. in an emergency situation. But a much better long-term solutions is to use a stand-alone generator that produces 120 V / 240 V.

Well, that was what I was thinking, that I’d keep the car engine running for an hour or two to keep the battery charged. Not a useful thing to do, usually, running the car in its parking spot (I imagine a hurricane blowing isn’t any fun to drive around in unnecessarily) but tell me more about these DC-to-AC inverters, as if I didn’t know a thing about them, because I don’t.

Where do I buy one? Do I ask for a DC-to-AC inverter? Am I going to be asked questions, like type do I want or which manufacturer? How do I hook one up? Any safety precautions I need to take?

I’ve kept my engine running in its spot by accident, btw. For a few hours. I bought a new car, keyless, last year and one day I forgot to hit the power button to turn it off and went inside and took a nap. I was surprised to find the car was running when I woke up.

There is a misconception many people have when they’re powering something from a vehicle’s battery with the vehicle’s engine running. In their mind they’re seeing it as the load (inverter + refrigerator or whatever) being powered from the battery, and the engine is simply keeping the battery charged. That’s not what’s happening. The load is not powered from the battery… it is powered from the alternator. The battery can be thought of as a big capacitor that simply minimizes the ripple voltage. All the power comes from the alternator.

We just had a thread about something similar

Let me try it again–I’m not being clear here. I’m asking about using a car battery to charge some sort of storage device (battery) where needed which can then provide power for my home (fridge, maybe, or lamp, computer, etc.), not running my home power directly off a running car engine.

actually maybe the most critical item I want powered during an outage is my CPAP machine, or maybe a fan if it gets hot with the AC out.

Using a car battery to charge another battery, and then using it to power a bunch of stuff? :face_with_raised_eyebrow:

Honestly, it sounds like you need a 120 V / 240 V generator (assuming you’re in the U.S.). I run all the critical loads in my house using a 4000 W Honda generator.

I’ve heard that a plug-in hybrid electric vehicle could be used as an emergency generator.

Yes. That’s why I was specific about the size of the inverter and the fact that it would only run for about 30 minutes on the battery alone. I intended my comment to be helpful only with respect to those two issues. In my experience, people tend to grossly over-estimate the inverter requirements for a fridge (e.g., that a pure sine wave inverter with 1500 watt capacity is essential).

They make portable battery units in various sizes and outputs these days. Jackery and Nexpow are 2 brands I have had good experience with. They are rated in watt hours and typically larger items like a fridge would need a larger battery capable of supplying more wattage.

In fact they typically talk about how long they can run a CPAP (typically without heating the air) in their description. Check them out on Amazon. You can also buy solar panels to recharge them.

I bought a medically-certified* battery specifically for my CPAP. I’ve used it in other camping-ish situations and it can run the machine for 3 nights, without heat of course. However, it must be part of a periodic charging routine (I recharge mine monthly).

*I don’t know if this is the right term, but some batteries are considered OK for medical use – presumably for reasons concerning gasses or spill resistance.

YouTuber Will Prowse has numerous and informative videos reviewing inverters and power sources of all sizes, from a few hundred watts to house-sized units. Most can be recharged from the grid, solar, a gas generator, or a car, although using the car is the least desirable option. The cost is closely related to the capacity.

I don’t know Will’s formal credentials, but he seems quite knowledgeable about the subject. He extensively tests what he reports on.

My CPAP is actually run on 12 VDC. The wall-wart just converts household current to 12 VDC.

When I go camping, I plug my CPAP into the cigarette lighter outlet. No problems so far. I did have to make an adapter. I suspect that they can be bought ready made. I had all the necessary parts to build mine in my junk pile.

Not that connecting to the internet will be a big priority in an emergency, but if you want to play Solitaire on your computer while the hurricane is raging outside, keep in mind that your typical generator AC is “dirty” and can cause problems with sensitive electronics. There are steps you can take to clean it, though.

Less common than it used to be. Lots of generators are ‘inverter’ systems now, and have clean output.