How Fast Will A Power Inverter Drain Battery? | A Little Math & a Lotta Useful Tips!

“How fast will a power inverter drain the battery?” is a common question for people using this alternative power source. A power inverter helps convert DC to AC, which you can use to power AC appliances like HVAC units, fridges, cookers, and microwaves.

Key Takeaways

  • You need to know how much energy a loaded inverter draws from the battery to understand the power consumption of your appliances.
  • Knowing how to reduce inverter energy draw from the battery is crucial to avoid running out of energy or flattening the battery.
  • Knowing the factors contributing to inverter battery drain helps keep your energy source intact.
  • It’s also crucial to have additional power sources like solar panels to ensure the batteries remain fully charged.

Inverters come in handy in an RV unit or if you prefer living off the grid. Although you get a steady flow of alternating current, power inverters are known to drain a car battery, especially when left on for long. This article answers how fast this happens and what to do to reduce the time frame.

How Fast Will A Power Inverter Drain Battery?

A small inverter consumes at least 0.2 Amps per hour without a load, while a large one consumes up to 2.0 Amps under similar circumstances. However, the figures might change depending on the battery’s conditions, as older batteries cannot hold much power for long.

That’s not all, as you still need to know a simple calculation on how much power a device with a load draws from the battery, how to reduce inverter drain, and things to consider when determining the inverter’s battery usage, which you will learn if you read on.

car battery and inverter

How to Calculate Inverter Power Usage with a Load

Sometimes you forget to unplug equipment overnight, which contributes to the overall power consumption and drains the battery voltage. Use this simple calculation to know how much your TV set or sound system consumes when left on overnight.

In this example, we will use a 300 watts load like a small AC unit and a 200AH car battery. We will also assume the inverter efficiency is at 90%, which is a common occurrence.

300w + 10% = 330w

330w/ 12V = 27.5 amps. An inverter with a 300w load draws 27.5 amps from a 12V battery. However, it uses lesser amps when connected to a 24V battery:

330w/24V = 13.75 amps.

Let’s find the actual hours it takes for a loaded inverter to drain the two setups by dividing the AH by AMPS:

200AH/27.5 amps = 7.2 hours

200AH/13.75 amps = 14.5 hours

Using these calculations, we can deduce that a loaded inverter requires 7 hours to ultimately draw a 12V battery and only 14 hours to drain a 24V battery.

For deep cycle batteries, deduct at least 20% or divide by half for ordinary batteries.

Remember that the power rating on the inverter doesn’t determine its energy usage but the load connected to the battery.

inverter in the car

How can you Reduce Inverter Energy Draw?

It’s frustrating to keep charging your battery, especially when you unplug energy-intensive loads like electronics. A fully charged battery can give you enough power to last days, only if you know how to minimize drain.

Try these tips to reduce battery drain and remain with enough wattage to run your devices:

Switch off the Inverter

Make it a habit of switching the inverter off when you’re not using power, especially when sleeping. If you must use an AC unit to cool or warm the RV, invest in a portable heater or fan with an independent power source. Such devices have a charging capability, which you can do during the day.

Invest in a Modern Power Gadget

If you have one of those old-model inverters, it’s time to upgrade to inverters with an auto-disconnect function. The device detects when the power is low and disconnects immediately, leaving you enough power in the system to run essential electronics.

Get an Optimal Inverter

Many people make the mistake of buying powerful inverters compared to the battery capacity. A powerful device draws much power from the battery when idling. A smaller inverter also means low power output, limiting your AC power. Try to strike a balance between the battery and inverter size.

Check Battery Capacity

Sometimes the inverter is not at fault, but the type of battery you’re using. An old and worn-out battery has a higher discharge ratio and will drain faster when connected to an inverter. If you suspect you’ll be on the road or off the grid longer than expected, investing in a deep-cycle battery capable of supplying you with consistent power is best.

You can have an additional deep-cycle battery if you need more energy. Such a setup is perfect for higher energy consumption projects or when you want more reserve capacity. You could also try a battery bank for more power supply.

Invest in Solar Panels

Solar panels are perfect for charging your batteries on a sunny day. You won’t need someone to jumpstart your car or even a semi-truck whenever you have a dead battery, which can be a lifesaver if you’re camping alone. The system is easy to set up and maintain.

The panels are perfect for people sealed off from the nearest civilization, offering an inexpensive power supply.

power inverter

Check the Vehicle’s Mechanics’

If you’ve been experiencing discharge lately, even after being on the road for long, check whether the alternator is functioning as needed. The work of the alternator is to generate electricity that charges the battery constantly when the vehicle is running.

Repairing or replacing this component could solve the problem.

Which Factors Determine Inverter Battery Usage?

A lot can contribute to the inverter draining the battery, with common problems ranging from a faulty inverter, an old battery, or a faulty circuit leading to energy loss.

However, here are the primary factors that cause the inverter to drain the battery:

Inverter Efficiency Level

As the inverter ages, or if you are running your power inverter all the time, its efficiency diminishes, causing it to drain the battery. You’ll start to notice a reduced battery run time, and where a battery used to run overnight, it now runs only a few hours.

The inverter’s efficiency level is how much energy gets lost when converting DC to AC. A suitable inverter should have a 90% efficiency.

Pure sine wave inverters are perfect for any off-grid living as they have a constant efficiency level. If you don’t have the money for a pure sine wave inverter, you can invest in modified sine wave inverters that perform equally but cost less.

Use the following formulas to calculate the power inverter efficiency level:

AC power output /DCpowerinput = Inverterefficiency%

Example: If you have a 1000W DC power source and your power inverter produces 900W AC, then the inverter has a 90% efficiency or a power factor of 1.11.

power inverter

Inverter Size

The size of your inverter plays a significant role in how fast it drains the battery. Small draining 0.2 amp inverters take approximately 60 hours to drain a 12V battery, while a big inverter drawing 2.0 amps takes less than 24 hours to drain the battery.

Load Size

Equipment like cookers, washing machines, and AC units require much power consumption, making it hard for one battery capacity to provide the needed energy. A homestead with huge appliances requires a powerful inverter, which increases the power inverter drain, especially if such power tools need to run overnight – see also 1500 Watt inverters.

Try reducing such equipment, and if that’s not an option, add more than one car battery to the system to increase power input.


Does an Inverter Damage a Car Battery?

An inverter can only damage the car battery if you make it a habit of leaving it on without any load. Recharging the battery more often after discharge damages the cells. Alternatively, misconnecting the inverter can cause reverse current flow or a short circuit.

Can You Power an Entire House with an Inverter?

No, you cannot power your entire house using an inverter, given that modern houses are full of power-intensive gadgets. However, you can use an inverter as a backup power source and disconnect any appliances that use a lot of energy.

Do You Need a Huge Battery for an Inverter to Work?

No, you don’t need a huge battery for an inverter to work. You only need a fully-charged 12V battery and know how to connect the setup.

Can You Connect More Than One Battery to an Inverter?

Yes, you can connect two or more batteries to an inverter. However, the batteries should be of the same voltage, i.e., 12V. Additionally, you need a powerful inverter that can handle the power surge. 

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