How to Know if Inverter Battery is Fully Charged

By:Michael Johns

how to know if inverter battery is charged

Inverter batteries are not the most user-friendly thing in the world.

They are a far cry from the sleek design we’ve come to expect in the modern world.

Deep cycle batteries don’t even have a built-in way to know if they’re charged.

So how do you know if an inverter battery is fully charged?

Well, you can use your inverter or a number of other external devices to find out.

In this article, we’ll go through the easiest ways to check if your inverter battery is charged, if it’s charging correctly, and how long recharging takes.

How to Check if Inverter Battery is Fully Charged

With no dials or meters on the battery, you need to use the devices you have hooked up to it in order to get a reading.

Use a Battery Charger

The best place to check is on your battery charger. All battery chargers will have a system to show where in the charge cycle you are. 

Very basic products just use 3 or 4 LED lights to give you a rough idea. A single LED would mean low battery while all LEDs lit up signals full charge.

More advanced battery chargers include a digital LCD screen to give you an accurate reading and tell you an exact charge percentage.

Measure Voltage (V)

Of course, you might not have a battery charger connected or available. This makes it important to know how much battery you have as it’s likely you don’t have access to recharging facilities right now.

Don’t worry.

The best way to monitor the battery charge level is by checking the voltage. This is because the output voltage is directly affected by the battery charge level. 

Let’s use a 12V battery for example. It will not always be exactly 12V. When a battery is fully charged it will have a voltage of over 13V while low charge it will be below 11V.

Voltage is the force of electricity. So when a battery is full of energy the voltage will be higher compared to low energy. 

Inverter Voltage Reading

If your inverter has a digital display then you will be able to tell if your battery is fully charged. All you need to do is look for the input voltage reading. When this reading is 12.6V or more (28V+ on a 24V battery), then you can consider the inverter battery fully charged. 

Check voltage on an inverter screen

LCD DC Battery Display

Keen to monitor the battery charge level independently from your inverter? You should install a dedicated battery monitor. This will give you an accurate reading of exactly how much energy you have. Depending on the product it can even tell you percentages and Ah level. Adding to this you can also monitor wattage, amperage, estimated runtime!

Use a Multimeter

One final option will give you a quick voltage reading to assess the charge state of your inverter battery. You can use a multimeter by hooking it up to the positive and negative terminals of your battery. To be honest, this is a quick way to tell the voltage but a bit fiddly to use on a regular basis. You’d be much better off with a display in your inverter or installed separately.

How to Check if a Battery is Charging Correctly

If you’re not sure whether your battery is charging correctly then you can easily tell by monitoring the voltage. You should see the voltage of a battery rise as more energy is stored in the battery. You can use any of the methods mentioned above to check.

Protip: You can still use your inverter while charging your battery. In fact, it has some great benefits.

Inverter Battery Charging Time

It’s impossible to give an exact amount of time it will take to charge your battery. This is affected by the battery size and what you are using to charge it. 

For example, you can get 50Ah, 100Ah, 200Ah batteries, and so on. Adding to this a solar panel will charge at a different speed to a rapid deep cycle charger.

To give you an idea you could fully charge a 100Ah battery with a 25A smart charger in 4 hours. If you use a 100W solar panel it would take 10 or more hours of peak sunlight for a 100Ah battery.

Final Thoughts on Checking an Inverter Battery is Fully Charged

It’s much easier to check if an inverter battery is fully charged by using the right equipment.

These batteries don’t come with any way to monitor the amount of energy stored so you will have to rely on either your charger, inverter, or separate monitor.

The voltage is a sure-fire way to know how well charged everything is. Remember high voltage means more energy and low voltage means less energy.

Need to replace your battery? Read my guide to the Best Battery for Inverter Use.