Ahhhh batteries, inverters, and runtimes…
It can be a bit of a nightmare trying to work out the best battery size for your 3000 watt inverter.
There are calculations to do and many questions that crop up along the way.
And to be honest, there are so many different pieces of advice out there that it becomes confusing.
That’s why I’ve written this complete guide to help you out.
Together we will go through battery size, power and energy requirements, and ultimately how long a 3000W inverter will run.
How Long Will a 3000 Watt Inverter Run?
A 3000 watt inverter will continue to run as long as you have enough energy in your batteries.
It is the energy capacity of your batteries and the appliances you run from your inverter that decide the runtime.
An inverter is simply a device used to convert the DC battery power into AC electricity for your electronics.
But don’t worry, we can easily work out how long your 3000 watt inverter will run. All we need to know is the total energy capacity of your battery and the amount of power you want to draw.
Once we know these two numbers we can divide the battery capacity by the power you want to draw.
1. Battery Energy Capacity
Battery sizes are measured in energy capacity. It should be clearly marked in amp-hours (Ah) on your battery the total energy at full charge – for example 100Ah, 150Ah, 200Ah, etc.
You will also need to know the battery voltage – usually, this is usually 12V.
2. Power Draw
The amount of power you draw will help to tell us how quickly you will use the battery energy. This is determined by the appliances you are running and not the inverter. With a 3000W inverter, you will usually draw much less than 3000W. For example, just running a TV would only draw about 70W.
So work out what appliances you want to run and the total wattage of these devices to find your power draw.
3. Runtime Calculation
Let’s do some example calculations. The equation you need to use are as follows:
First, we need to get a final number of how much energy you will use per hour. To find this you divide your watts by volts. Let’s assume you are drawing max load of 3000W at 12V.
3000W ÷ 12V = 250A. At full load, you will use 250 amps an hour (Ah).
Now you just need to divide your battery size by the 250Ah you will use. Let’s say you have a 300Ah battery.
300 ÷ 250 = 1.2 hours. Drawing 3000 watts from a 300Ah battery will run for a maximum of 1.2 hours.
If you reduce your power draw to 2000 watts, you would increase your runtime to nearly 2 hours! Remember, a 3000W inverter won’t always draw maximum power, it depends what appliances you are running.
To sum up: You need to do two calculations.
- Watts ÷ Volts = Inverter Amps.
- Battery Ah ÷ Inverter Amps = Runtime.
How Many Batteries for a 3000 Watt Inverter?
In my experience, you will need a very minimum of 300Ah battery capacity with a 3000 watt inverter.
Now you know how to calculate inverter runtime you can decide what size battery you need. It is likely you will need multiple batteries to give you enough energy for a 3000 watt inverter.
Common battery sizes are 50Ah, 100Ah, 150Ah, 200Ah, 250Ah, and 300Ah. It is hard to get a single battery bigger than 300Ah as they become incredibly heavy and cumbersome. So to get more capacity you can hook up multiple batteries to an inverter.
To work out how many batteries you need for a 3000 watt inverter you just need to know how many amps your inverter uses each hour. (The same equation as above: running Watts ÷ Volts = Inverter Amps).
Then you just multiply your inverter amps by the runtime you need. For example, if you need to draw 150Amps for 3 hours you need a 450Ah battery. 150 x 3 = 450Ah.
As you can’t get batteries this big you could instead get three 150Ah batteries and link them together.
Discharge Capacity
I just want to add a quick word on battery discharge capacity. Regular lead-acid batteries have a discharge capacity of 50%. This means you should not discharge them more than 50%. Running a lead-acid battery low will cause it to be damaged.
This means you can only use half the energy stored in a lead-acid battery. So you need to double your battery capacity.
It can be quite annoying so you might consider getting a more modern lithium battery that has a 100% discharge capacity and recharges more quickly. (It’s the type of battery you get in smartphones).
3000 Watt Inverter Battery Size Chart
Here’s a handy chart to help you quickly calculate how long a 3000W inverter will run on 12V batteries. I have included multiple maximum runtimes based on the number of watts drawn with your inverter.
| Runtime 3000 Watts | Runtime 2000 Watts | Runtime 1000 Watts | Runtime 500 Watts | Lead Acid (50% Discharge Capacity) | Lithium (100% Discharge Capacity) |
| 20 mins | 30 mins | 1 hour | 2 hours | 200Ah | 100Ah |
| 45 mins | 1 hour | 2 hours | 4 hours | 400Ah | 200Ah |
| 2 hours | 2.5 hours | 5 hours | 10 hours | 1000Ah | 500Ah |
| 4 hours | 5 hours | 10 hours | 20 hours | 2000Ah | 1000Ah |
| 6 hours | 7.5 hours | 15 hours | 30 hours | 3000Ah | 1500Ah |
| 9.5 hours | 12 hours | 24 hours | 48 hours | 4800Ah | 2400Ah |
What Will a 3000 Watt Inverter and Battery Run?
By now you might be wondering what a 3000 watt inverter can power?
Well, the answer is a lot!
With this power capacity, you could happily run most home appliances including coffee makers, refrigerators, washing machines, lights, computers, TVs, toasters, and games consoles. You won’t be able to run all of these at once, but you could certainly run at least 1 or 2 at a time.
Adding to this you will also be able to charge phones, laptops, tablets, digital cameras, and other gadgets. Here’s a selection of appliances and their average wattage:
| Appliance | Average wattage |
| Phone | 5 |
| Tablet | 10 |
| Laptop | 30-60 |
| Mini-fridge | 40-70 |
| TV | 50-80 |
| Games Console | 100-200 |
| Refrigerator | 300-500 |
| Microwave | 700 |
| Toaster | 1200 |
| Washing machine | 1000-2000 |
| Coffee maker | 1000-1500 |
| Compressor | 2000 – 3000 |
| Clothes Dryer | 2000 – 2500 |
| Heater | 2000 – 2500 |
If you want to run more than one appliance at the same time, simply add together the total watts to know the power requirement.
Inverter Efficiency
The efficiency of your inverter is one other thing to be aware of. Inverters are not 100% efficient, usually, they are about 85% to 95% efficient. This is because they lose energy during the conversion of DC to AC plus use power for internal systems.
It is best practice not to draw more than 80% of the total inverter wattage capacity to avoid overloading.
All of the calculations above give you an estimate of runtime and battery requirements. The amount of energy appliances use varies all the time, plus nothing is ever perfectly efficient. So when making your calculations always give yourself extra capacity and energy to keep you covered.
What Size Battery Cable for 3000W Inverter?
When you buy an inverter it should arrive with the correct size cables to hook up to your battery. Of course, these might need replacing or you might want to connect multiple batteries together. In this case, you need to make sure you have the right size AWG cables.
The most common size cable for a 3000 watt inverter is 4/0 AWG.
It is not a set rule as the gauge of wire changes depending on length.
Final Words on Batteries for a 3000 Watt Inverter
To be honest, 3000 Watt inverters are pretty big so you will need a minimum of 300Ah battery capacity in my experience.
There is no exact answer to how long a 3000 watt inverter will run or how many batteries you need for a 3000 watt inverter.
It all depends on the amount of energy you are using and for the length of time.
The information above should help you to calculate the answers for your own personal needs.
The products recommended will give you a great starting point to find the equipment for success.
