How Many Hours can a Power Inverter Last?

There are many uses and occasions that a power inverter can come in handy. It could be that you are planning on tail gating outside of your favorite football stadium and you need a way to plug-in your crockpot. Or, you are going on a long road trip and want to bring a television or computer to keep the kids entertained. Or, it could be as simple as wanting a warm cup of coffee after camping out in the woods.

Whatever your reason for using them power inverters are a versatile tool that can provide you with needed alternating current (AC) power. AC power is what we use to power everything in our home, office, and other buildings. Your vehicles on the other hand use a different type of power known as direct current (DC) power. DC power is produced by your alternator and is stored in your vehicle’s battery. Stored DC power gives you enough power to start the vehicle, play the radio, turn on the interior lights, and other smaller things.

In order to operate an AC appliance or electronic in your vehicle you will need a power inverter. The inverter converts the DC energy over to AC energy. This is done by hooking directly to your battery on one end and on the other end having a standard one-hundred and twenty volt outlet. Over the past few weeks here at we have been doing article after article on the topic of power inverters. There are many questions to be answered on this topic and today’s topic is just how long can you expect a power inverter to operate?

How Many Hours Can They Last?

Like with many similar topics there is not a clear cut answer here. There are many variables that have to be considered here before we can give you a timeline. The first question I am going to ask you here is how do you plan on running your power inverter? Will your engine be running while running the inverter or off? This is a KEY question as the answer can radically alter the length of the power inverter usage.

Earlier we mentioned that the alternator in your vehicle charges the battery as you are driving or while the engine is idling. The battery then stores this DC energy produced from the alternator. When you go to start the car the stored energy is used to turn everything on and then the alternator takes over again. When a power inverter is running it draws its power from the stored DC energy in your battery. If the vehicle is off while you are running the inverter then that means you are solely relying on your battery for your power source.

Your standard twelve volt automotive battery is NOT meant for long term use like this. Instead they are meant for short bursts of energy like starting your vehicle. They should not fall below ninety percent capacity. If they do then you risk damaging the battery or even killing the battery leaving you stranded. So, if you are running an inverter based on your battery’s energy then you can really only expect about thirty to sixty minutes of use before your battery dies.

Engine Off

This is exactly why I recommend not running your inverter with your engine off. If you are going to be tailgating though and will need power for hours at a time there is an alternative solution. Earlier I stated that the standard battery is only good at ninety percent capacity or higher and that they do not last long under a power inverter load. What you can do though is look at installing a secondary battery for your vehicle. This secondary battery will be charged by your alternator just like the other but it will give you an alternative source of power for your power inverter. When going this route it is key that you purchase deep cycle battery as your secondary battery.

Deep cycle batteries are intended for long term usage. They can be used for hours, sometimes even days, at a time. They can fall as low as fifty percent capacity as well. One key thing to mention here is that you will need BOTH a standard cranking battery AND a deep cycle battery. The cranking battery is necessary to start your car and the deep cycle is used to power your power inverter. Another point to mention here is that deep cycles can take a significant amount of time to charge. Because of this some folks will opt for a higher output alternator as well. Remember that both batteries have to be charged by your alternator and if you have a higher output alternator then you will be able to charge both batteries faster.

Installing a secondary battery can be a bit tricky. If you are an experienced tinkerer with vehicles the you should be able to handle it by following this guide that I found. However, if you are no as comfortable working on vehicles then I recommend taking your vehicle into the dealership or a local mechanic and tell them that you want a secondary deep cycle battery installed. If you also already have the power inverter purchased you can ask them to install it as well. Otherwise, you can install it after the fact.

Engine On

If you are in the situation where you are going on a long road trip and need a power source for a television, computer, or whatever else then you are in luck! In my opinion the best way to run a power inverter is with your engine on while driving down the road. This gives you a high number of rotations per minute which allows your alternator to produce maximum direct current electricity which is then fed into your battery. While the alternator does produce energy while the car is idling you are going to be much more efficient while driving at highway speeds.

By using the inverter while your engine is on and the vehicle is moving the power inverter will produce power to your appliances indefinitely. At least until your engine runs out of gas or the engine is turned off. This is why I recommend this approach so much as it gives the power you need and all but eliminates the risk of draining your battery while running the inverter. With the engine on your battery is constantly being recharged.

There are instances though where you can overload your alternator and your battery. Say for example you hook up a three-thousand watt power inverter to your vehicle. You do NOT have a high-output alternator and you do not have a secondary battery installed. It is a standard system with a large inverter hooked dup to it. If you are running this inverter and have thousands of watts of appliances plugged into it while driving you could actually overload your alternators output. When this occurs the alternator attempts to compensate for the overage by drawing power from your battery. If this occurs you could actually end up killing your battery as you drive down the road. Not a good situation to be in.

Sizing & Power Draw

The size of the power inverter and the appliances you will be plugging into it matter quite a bit. If you are using a three-hundred watt inverter to power your laptop as you drive down the road then you will not notice any change at all. It is a very small wattage draw. However, if you are in the situation we mentioned earlier with a three-thousand watt inverter and are trying to operate a band saw as you drive down the road… then you are most likely going to overload your alternator and battery. I sincerely hope you are not planning on doing this though…

The point here folks is that the size of your inverter along with the size of the appliances that you will be plugging into them can impact just how long the inverter can and will run. We had stated that with your engine off you could expect a standard battery to last about thirty to sixty minutes with an inverter connected to it. Well, that may be for a laptop or coffee machine… but if you plug-in a power tool then you that thirty minutes may only turn into five or ten. The amount of power you draw from your battery will determine how long it will last.

Power inverters come in all sorts of sizes ranging from a few hundred watts all the way up to four or five-thousand watts. To determine the size you need you need to add up all of the wattage requirements of each and every appliance or electronic that you wish to run off of the inverter. Some of these may have a total wattage draw label but others may not. No need to worry though as you can determine this by finding the total amperage draw on the appliance. When you have the amps simply multiply it by the volts. Volts are very easy to find, in fact if the appliance plugs into a standard out let then you have the volts. One-hundred and twenty volt outlet. As an example, let’s say you have a six amp coffee maker. Six amps times one-hundred and twenty volts equals seven-hundred and twenty watts to run the appliance.

We typically recommend going twenty or thirty percent higher then your calculations as well. This gives you a buffer in case you miscalculated or if you want to add something else later on. In the coffee machine example above you would need around a one-thousand watt power inverter factoring in the extra thirty percent. Our recommend inverter at this size is the Ampeak model that can be found on Amazon by clicking here. It is set at an aggressive price and has over a thousand reviews to ensure you get an adequate product.

One last point to mention here on sizing an inverter. If you are not using your inverter be sure to turn it off. Depending on the model it can still pull five to ten percent of its rated wattage even if there is nothing plugged into it. By turning it off you are ensuring that there is no drain on your battery when it is not in use. Always better to be safe then sorry and end up with a dead battery on your hands!


As you can see folks there is a lot that goes into determining just how long a power inverter will last. I wish there was a clear cut answer I could give you but inverters just do not work that way. Either way, I hope this article was able to point you in the right direction and allow you to figure out how you want to run your power inverter.

Thanks for reading,

Alec Johnson

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