How fast will power inverter drain battery? We answer

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So, how fast will power inverter drain battery? We tell you in this article

Long gone are the days when power inverters would suck the life out of batteries before you even knew it (thanks to today’s much advanced semiconductor technology).

That said, it’s still nice to have an idea of the maximum running time you can expect from the battery-power inverter combo.

Certainly, you would be able to plan for your emergency or off-grid power needs better.

Here are some tips to help you figure out how fast your power inverter will drain the battery:

How fast will power inverter drain battery?

Now, I must say that there is no single answer to how long a power inverter will take to discharge a battery.

That’s because there are by far too many variables that determine the amount of energy used by the inverter setup off the battery.

These factors include the items you have plugged into both the inverter and battery (and their consumption), the battery’s voltage (of course, bigger batteries operate longer), and more.

Also, don’t forget that an inverter isn’t 100% efficient due to the DC-AC conversion process.

In fact, research has shown that the inefficiencies are widely varying among different inverter models.

Another important thing to keep in mind is that improper wiring of the system during installation could greatly reduce your battery’s running time when inverting.

In short, you need to have some background information at hand to know exactly how long your battery will last.

That said, you can take a mathematical approach when working out the number of hours the battery (or bank of batteries) will power the inverter.

Read about it next….

How fast will power inverter drain battery ?

Answer: Use the formula method to estimate the duration your batteries will serve

Apply the following formulas to take some of the guesswork out of the question.

Simply insert the total wattage of the devices you’ll be powering off the inverter along with the reserve capacity of the battery into the applicable formula:

For those using 12 Volt batteries:

Approximate running hours= (10 x (the Battery Capacity in Amp-Hours) ÷ (Total Load in Watts)) ÷2

Example: You have a 100 AH rated deep cycle battery and you want to keep the following gadgets running:

  • Small Table Fan – 30 Watts
  • 32-Inch LED TV – 41 watts
  • video game console – 90 watts
  • Laptop -50 watts

How long will it take to deplete the battery?


Work out the total energy consumption first..

Total Load in Watts = 211 (30 + 41+ 90+ 50)

Then compute the expected running hours= 10 x (100 ÷ 211) ÷2 = 2.36 hours

You will get 2 hours and almost 22 minutes out of your 100 AH battery.

For those using 24 Volt batteries:

Approximate running hours= (20 x (the Battery Capacity in Amp-Hours) ÷ (Total Load in Watts)) ÷ 2

Example: If you’re using a 24V system (150 AH) for the same applications, what should be your projected hours?


You again substitute the numbers in the formula….

Run time in hours= 20 x (150 ÷ 211) ÷2 = 7.1 hours (the battery won’t run down as fast as above).

Now that you know, it’s advisable to be a little pessimistic in your run time expectations as a precautionary measure.

We have already seen that inefficiencies from the inverter (it draws some power even when you’re not applying  any load) eats into the battery juice so expecting 6.8 hours (for example) instead of 7.1 hours makes a lot of sense.


  • You can check the wattage required by appliances from the user’s manual (it’s also sometimes shown on the device label itself).
  • Deep cycle batteries tend to higher reserve ratings.
  • Heavy duty loads—the likes of desktop PCs, big TVs, and such—will run down the battery more quickly than conservative electronics.


How to make your battery run longer when inverting

Here is the thing: there are some small tricks and hacks that you can implement and make your battery supply energy to the inverter for much longer.

Try these handy steps:

  1. Turn the things that are not essential off. Obviously, removing the entire unnecessary load will give you a couple of extra minutes or even hours.
  2. Keep the extension cord and the whole DC circuit as short as practically possible when installing. This eliminates a bit of the resistance and may help reduce the rate at which the battery depletes.
  3. Make use of the power-saving features in the inverter. Most best-selling inverters have a power saver mode that minimizes energy usage from your battery bank when turned on.
  4. On a related note, some electronics have settings that can help further save energy. You can, for example, lower the amount of energy your TV draws by turning the brightness of the LCD screen down.
  5. Use the inverter while the battery is being charged by third-party charging solutions such as the car or a generator (the type with built-in battery chargers).
  6. Also, consider hedging your bets against a dead battery by bringing an additional deep-cycle battery with you (or connecting multiple batteries in parallel) if your solar battery drains fast.


How fast will power inverter drain battery: Other related questions

Does an inverter drain a battery even if it is shut off?

In general, an inverter doesn’t draw current when powered off and shutting it down is a good way of making your battery run for more hours when you need it to.


So, again how fast will power inverter drain battery (or how long can a battery run an inverter)?

Short answer: the length of time your inverter can feed from the batt depends on a whole world of factors- the battery size, the applied load, inverter efficiency (the standard is about 10%), and such.

But the best way to get a rough estimate is by using the formulas (10 x (the Battery Capacity in Amp-Hours) ÷ (Total Load in Watts)) ÷2 for 12 volt systems and (20 x (the Battery Capacity in Amp-Hours) ÷ (Total Load in Watts)) ÷ 2 for 24 volts systems.

Refer to the illustration we gave earlier to understand how they work.

Everything said, do not allow your batteries to discharge below the recommended charged state level (depth of discharge) which is 50% in nearly all deep cycle batteries.

Doing so risks shortening the life of the battery significantly.


So, what will a 400 watt power inverter run?


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