How Many Batteries Do I Need For a 1000 Watt Inverter?

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In RVs and off grid homes, the inverter is connected to the battery bank and uses it power AC appliances and devices. Even in a grid tied setup, you may want to use batteries as a backup power source. So how many should you get?

A 100ah battery can run a 1000 watt inverter at full power for an hour before it is completely drained. If the battery has a 50% discharge rate, the inverter runtime will be reduced in half, so the battery size has to be doubled to 200ah to run for an hour.

1000 Watt Inverter Battery Requirements

The batteries required depends on how long the inverter needs to run, and how much load it carries per hour of runtime. Inverter efficiency has to be accounted for as well.

To calculate, use this:

Inverter watt load / volts = amps per hour

and then:

battery size / amps per hour = runtime

If you have a 1000 watt inverter and want to run a full load for one hour, it will draw 83.3 amps.

1000 watts / 12V = 83.3

You need an 83ah battery, but you should get a 100ah battery to compensate for inverter inefficiency.

100ah battery / 83.3 amps = 1.2 hours

You get a runtime of 1.2 hours. But batteries discharge faster the more amps are drawn, so expect the battery to drain after an hour.

We emphasize that a 100ah battery will be fully drained after running the inverter for 60 minutes. If you use lead acid batteries it must be recharged when the capacity drops to 50%. If you are looking for a 100ah battery, we recommend the Weize 12V Deep Cycle AGM since it works with all kinds of inverters and in different setups.

If you want to run a 1000 watt inverter for an hour on a 12V lead acid battery, get 200ah. By the time it drops to 50% the inverter would have run for the prescribed period. Our top pick is the Renogy 12V AGM 200 as it is tailor made for inverters.

This formula is applicable regardless of the inverter or battery size. Just substitute the amps and watts with your own numbers and round off the results to the next largest battery capacity.

1000 Watt Inverter Battery Chart

This chart shows what battery sizes to use to run a 1000 watt inverter at maximum load. If you are going to use a lead acid battery, use the third column as a guide because they should not be drained below 50%. This chart assumes the inverter will run a full 1000 watt capacity. If it will carry a 500 watt load for 30 minutes for instance, a smaller battery will suffice.

Runtime with 1000W LoadBattery Size (100% Discharge)Battery Size (50% Discharge)
1 Hour100ah200ah
2 Hours200ah400ah
5 Hours500ah1000ah
12 Hours1000ah2000ah
24 Hours2000ah4000ah

Some AGM batteries have a 70% DOD, but most FLAs are at 50%. If you have lithium batteries you can drain it completely. They do cost more though, which can be an issue if you need several.

If you have a 1000 watt load that needs to run for 30 minutes, a 100ah battery is fine. When calculating inverter sizes , it is all about the load that it must run and the depth discharge.

The longer you have to run the inverter, the more batteries you will need. An off the grid home may run on solar panels during the day and batteries at night. However, any appliance that runs on AC -which is most – will always need to run on an inverter.

This brings us to the next question, that is how long can a battery last. As you will see that will depend on several factors.

How Long Will a 12V Battery Last with a 1000 Watt Inverter?

The inverter load will determine how long a battery will last and whether the battery will be completely discharged or not.

A 400ah deep cycle battery will last 4 hours with a 1000 watt inverter before it is fully discharged. If the battery is discharged at 50% the inverter will stop running after 2 hours.

Even though you can recharge lead acid batteries on electricity, the 50% depth discharge rule still applies. To avoid complications the battery size should be double what you need.

If your inverter has to carry a full load for 2 hours, get a 400ah lead acid battery. Even if you have to recharge when the level drops to the halfway mark, the inverter can still use around 166 amps, more than enough.

Another option is to use a lithium battery bank. Yes it will cost you more but the trade off is a higher discharge rate. If you always use the inverter for long periods, recharging constantly can be a hindrance. With a lithium battery you have almost full use of its power.

When choosing batteries, always opt for the next biggest size you can get. If the inverter needs 83 amps an hour, get a 100ah battery. If you need 135ah, go with 150ah or 200ah. Having reserve power is important in case of a power surge.

What Will a 1000 Watt Inverter Run?

A 1000 watt inverter can produce up to 1000 watts an hour. That is a lot of power and can met the needs of a small camper.

A 1000 watt inverter can run a TV, laptop, printer, game consoles, hair dryers, a microwave, vacuum, blender, fan, lights and many more. Here are some examples.

  • If you are going to run just one appliance, it is easy. An average laptop uses 200 watts an hour. With a 1000 watt inverter, you can run it for 4 to 5 hours.
  • A 50 inch TV draws 3.7 amps an hour. Multiply 3.7 amps x 120V = 444 watts. Your inverter is good for about two hours.
  • A dehumidifier consumes around 800 watts, so you have around 1 hour and 15 minutes of use.

Here are some other appliances:

  • Blender 400W
  • Printer 100W
  • Desktop Computer 400W
  • Ceiling Fan 120W
  • Chest Freezer 600W
  • Light Bulb 25W
  • Slow Cooker 270W

By adding the total watts or amps drawn per hour, you will have a good estimate of how many appliances the inverter can run and for how long. In an off grid system this all depends on how many batteries are connected to the inverter and the depth discharge.

A 1000W inverter may be sufficient for RVs. Most RVers have an additional power source like a generator, and if you spend most of your time in the campgrounds you will not need a lot of battery power anyway.

But if you like to boondock in far off locations, an inverter of this size – with matching batteries and solar panels – is likely sufficient. Of course it will depend on what additional power sources you have and their capacity.

Running and Surge Watts

Running watts is the power used by a device as it operates. The surge watts is how power the device requires to start up.

Take a hair dryer. Most use 1000 watts to run, which your inverter can handle. But its surge or startup watts is 2000 watts, double the inverter capacity. This surge only takes a second, but without it the hair dryer will not run.

A 1/2 HP motor might require 870 watts to operate, but to start it up, the inverter must supply 2000 to 2500 watts. And there are many other appliances, tools and devices with high surge watts.

Before running any appliance on a 1000 watt inverter, check its surge watts. If it is over 1000 watts, the inverter will not be able to run it, regardless of the running watts.

Even if your inverter can handle 1000 watts, it is not a good idea to push it to the limit. Running at full load a few times is all right. But if you find that you are constantly using up 1000 watts ,maybe it is time to get a larger inverter.

1000 Watt Inverter Efficiency

When an inverter converts DC into AC power, some power is lost due to inefficiency. It is similar to solar panels, which cannot 100% convert sunlight into solar power.

Inverter efficiency ratings vary, but 85% is the minimum acceptable. Better quality inverters have a 95% rating, which is the range you should aim for. The higher the rating, the longer the inverter can run on a high load.

The problem with a low efficiency rating is it affects inverter performance. A 15% energy loss for instance, means less than 1000 watts are usable, probably 900 watts or even lower. So you have to make sure the inverter quality is high.

What Inverter Type Should I Use?

Pure sine wave inverter is superior to modified sine wave inverters, offering better performance, less energy loss and longer lifespan. However, modified sine wave is more affordable and still widely used.

If you re going to run power tools and other sensitive devices, go with pure sine. You will want the most effective inverter for these components, so consider it an investment. If you only use the inverter a few times and for short periods, modified sine wave will do.


Inverter battery power demands depend on the load it has to carry. By knowing how to calculate the number of batteries needed, you will be able to get the exact figure without buying too many or too few.