How Fast Will a Power Inverter My Drain Battery?

If you're thinking of buying a power inverter one of the first questions that you probably have is how long will it take to drain you battery.

Answering this fundamental question will ensure that you purchase the correct size power inverter for your needs, and that will know what you can run from your power inverter, and for how long.

Different things can influence the ability of the battery to power up gadgets and appliances, and the power inverter’s features can be one of them. We would want the battery life of our devices to be extended as long as we possibly could.

This article will guide you more on how to make the most of your battery life, and how fast power inverters will drain them. 

Power Inverter Characteristics that Affect Battery Life 

So how fast will a power inverter drain your battery?

A better way of asking this question would be how long would you want your load to run. By asking this question, you’re able to make specific calculations that can help you determine the ideal size of your battery bank.

The amount of time that your appliance will operate will also depend on its power consumption that’s usually measured in watts and battery capacity.

It’s also important to note that inverter inefficiency and improper wiring of the battery during installation can greatly reduce your appliance’s running time, so make sure you are taking expert advice when installing. 

Units for Measuring Electricity Features 

One good way of knowing the watt measurement is by multiplying volts by amps. Your battery’s capacity can also be expressed by the number of amps and how many hours your battery will last. This is referred to as the Amp-Hour or A.H. capacity.

Every 100 watts of a 12-volt inverter system needs around 10 DC amps from its battery. Meanwhile, a 24-volt inverter system needs a battery’s 10 DC Amps for every 200 watts. These figures are important to remember because these are where your battery’s efficiency depends on.

You can know how long your power inverter’s battery will last if you estimate the load’s total watts. Also look at an appliance’s input electrical nameplate and add up its total requirement. This gives you a hint on how much power your appliance can take.

However, there are a few loads that aren't constant, which is why it is important for them to get estimations. Take for example a refrigerator that's powered by a 750-watt compressor. If it runs 1/3 of the time, then it would be running around 250 watts per hour.

The size of the battery bank can then be calculated once the running time and load are established. To do this, you first need to divide its watts load by 10. This is if your appliance runs on a 12-volt system. If it runs on a 24-volt system then divide it by 20.

Meanwhile, the amount of time that you use your power inverter to run your appliances will depend on your battery’s power capacity.

Use this formula to know how long your power inverter’s battery will last:

(10 x [Battery Capacity] / [Load]) / 2

However, you need to know your appliance’s wattage and battery’s reserve capacity before you can input the figures in the formula. So, for example, if your battery has a 100 amp hour capacity and you’re going to use it on a laptop that uses only 45 watts, then you’re going to get around 11 hours of working time from your battery.

The formula then becomes like this:

(10 x [100 AH] / [45 Watts]) / 2 = 11.11 hour

However, you still need to be cautious when dealing with your inverter even if you already know the figures. This is because if you're going to, let's say, force a 45-watt load to run for 11 hours in a 100 AH battery; there's a huge likelihood that there won't be enough power left to beef up the starter motor.

This also means that appliances with bigger loads such as desktop computers, televisions, and other electronics will drain your battery faster.

Working Example

In order for us to better understand the capacities of our car batteries, and how these inverters will most definitely impact its life, then let's have a real-life case study that focuses on all of this by-the-numbers.

For this study, let's have a look at the time for an average car engine start battery, which has a 60 Ah, or Ampere-hour rating will be able to run a TV with an average rating of 100 Watts. The car engine battery also has a PW150 rating.

This means that the load falls within the maximum power of the PROwatt inverter. Because of this, the inverter will not be a limiting factor for the run-time of the TV. This is a common scenario in people with trailer homes, as well as truck drivers who want better entertainment to accompany them on the road.

Putting the numbers into consideration, we have 10, multiplied by 60 Ah, multiplied by 100 W.

This means that the TV can run for a maximum of 6 hours before the battery gets discharged completely, and for more comfortable viewing, and making sure that the car can still be started, 3 hours’ worth of run-time to the half-way point of the battery.

Of course, you would not want your car battery to be drained, lest it would not go on running. 

Some Tips Worth Keeping in Mind

Starter batteries for the engine should not have a discharge rate lower than 90% of the remaining, and for marine batteries that are deep cycle, it should not be lower than 50%. This is because any rates lower than these would cause the life of the battery to be shortened, and is also prescribed by a lot of battery manufacturers.

In the case of the PROwatt250, it comes with a lighter plug that allows for easier load connection, especially between smaller ones. A direct connection, however, is needed if you want to load for 100 W and above to battery terminals. This will help to reduce the amount of voltage that gets lost with thin and long battery wires. Lesser voltage wasted ultimately means a shorter time to run the whole system.

If you want to use power tools for purposes other than home use, or for loads of 200W for applications greater than an hour, an auxiliary battery may be needed to give power to the inverter.

Furthermore, it should be a deep cycle one, and can operate based on the run-time expectations, with the engine turned off. Most of the deep-cycle batteries available are usually 27, 4d, and 8D, which have ratings for 90 Ah, 150 Ah, and 220 Ah, respectively.

Lastly, the alternator should not be attached to the auxiliary battery via an isolator module, as doing so will cause the inverter to discharge the engine start battery even when it is turned off, which can cause you to waste a lot of electricity needlessly.