They are a series of small Light Emitting Diodes (LED’s) that run along a string similar to Christmas Lights.

However, christmas lights use bigger, much larger LEDs compared to fairy lights. 

Due to the size of the LEDs used in fairy lights, they aren’t used to illuminate spaces but rather used as decoration. 

Fairy lights are designed to be powered with batteries as they are used in applications away from power sources as well as to make them a bit more aesthetically pleasing. 

But, how long do batteries last in fairy lights? The standard batteries that come with fairy lights last around 5- 25 hours depending on the length of the fairy lights. Below is a table summarizing the different lengths and how long the batteries will last. Note, this is an estimate based on calculations in an ideal situation.

However, how long  batteries last in fairy lights comes down to many factors which include;

• Battery capacity
• Current consumption of  the LEDs used in the fairy light
• Length of fairy lights (more lights = greater current consumption) 
• Quality of batteries 
• How long the fairy lights are used for 

In the following article I will list in more detail these factors and give you guidelines on how to roughly calculate how long the batteries and fairy lights you are using will last. 

As, not all the factors will be the same for everyone, values will vary.

Factors that affect how long batteries last in fairy lights

The value of 5 – 25 hours that I mentioned earlier is just an estimate of how long standard Coin cell batteries, plus a standard set of fairy lights will last for. 

But, there are many other factors that play a part in determining whether the batteries will last for a longer or shorter amount of time. 

Let’s take a look at them.

Factor #1 of how long batteries last in fairy lights: Battery capacity

The first major factor which has a large influence on how long batteries in fairy lights last for is the Battery’s Capacity. 

Battery capacity is defined as the amount of charge a battery can hold.

A great analogy for this is a car’s fuel tank.

Some cars have bigger fuel tanks than others, giving them the ability to hold more fuel and thus allow them to travel farther. 

This is the same for a battery. 

However, while physical dimension does play a role in determining it’s capacity, Chemical composition plays a big role too. 

An important value that indicates a battery’s capacity is it’s Amp-Hour (Ah) or milliamp-Hour (mAh) rating.

These ratings tell us how many amperes( or milliamperes) a battery can supply for one hour. Bigger batteries will tend to have their ratings in Ah, while smaller batteries will have it in mAh. 

For example, let’s say we have a AA sized battery which has a battery capacity of 500mAh.

This tells us that the battery can deliver up to 500mA for an hour or, 100mA for 5 hours, or 50mA for 10 hours.

To calculate how long a battery will last (in hours), we divide its capacity by the current draw of the circuit.

This rating will ultimately determine how long those batteries in your fairy lights will last for which can be found on most batteries. 

If the battery does not display these values, you can search the brand of battery online and check its datasheet which should indicate its battery capacity.

The higher the Ah/mAh rating the battery has, the more charge it can hold. 

Factor #2  of how long batteries last in fairy lights: Current consumption of Lights

The battery’s capacity is only one part of the equation when it comes to how long it will last when powering electronic devices such as fairy lights.

The second factor is Current Consumption of the lights used in fairy lights. 

An example would be the best way to illustrate this. 

Let’s use the same battery capacity in the previous example of 500mAh.

This time the battery will be powering two different light sources, both of which have different current consumptions.

As you can see the battery capacity is the same in both scenarios, however, how long the battery lasts for changes. 

This is due to the different currents required by each LED in each scenario. 

The LED in scenario A consumes 50mA and therefore the battery will last for 10 hours.

Whereas, the LED in scenario B consumes 100mA which means it will last for 5 hours.

A 50% decrease in time. 

So, the amount of current the type of light used in fairy lights consumes, plays a large part in how long the battery will last for. 

Different types of fairy lights

Fairy lights use Light Emitting Diodes (LED’s).

But, LEDs vary in size, colour, brightness, angle of illumination etc.

Depending on the LED’s characteristic, it will draw different amounts of current. 

A smaller LED will require much less current to operate compared to a bigger one. 

Also, the brighter the LED, the more current it will draw which is going to drain a battery much faster. 

Factor #3  of how long batteries last in fairy lights: Length of fairy lights

Next on the list of factors that affect how long batteries will last in your fairy lights, is its length.

Fairy lights come in a variety of lengths from 1m, 2m, 3m, 5m and more. 

How does the length affect the battery?

Increasing the length means the number of LED’s are going to increase across the length of the fairy light.

The more LEDs are going to add to the overall power consumption (which comes down to some electronics theory). 

In a Series circuit the current supplied by the battery remains the same throughout the circuit, but the voltage is divided among the components. 

Adding more components such as LED’s is going to increase the power consumption of the overall circuit. 

We saw earlier the current capacity of a battery given in Amp-Hours, or milliamp-hours. 

But, to calculate more effectively how long a battery will last with multiple LEDs it is better to look at the battery’s Power capacity (Wh). 

To obtain the power capacity we simply multiply the current capacity of the battery by its nominal voltage. 

Say, we have a 3V battery whose current capacity is 250mAh, its power capacity will be 750mWh or 0.75Wh.

Let’s take a look at a quick example.

Below is a circuit with a voltage supply and one single LED.

To calculate how much power the LED consumes we use the power formula; P = V x I.

Giving a power value of 34mW for the LED.

The power capacity of the battery is 750mWh (3V x 250mAh).

Dividing the power capacity of the battery (750mWh) by the power consumed by the LED (34mW) gives us the value of how long the battery will last for which equals 22 hours. 

Now let’s add another LED as seen below.

The voltage and current capacity of the battery remain the same. 

But, by adding a second LED (of the same value), the overall power consumption of the battery is doubled (34mW x 2 = 68mW).
Now, when we divide the power capacity of the battery by the overall power consumption of the two LEDs, we get 11 hours.

Note, as you add more LEDs, the voltage drop across is going to increase. To combat this, you will need to increase the value of the supply voltage. 

This is why fairy lights greater than 2m (6.5ft) in length, will require more batteries. 

Factor #4 of how long batteries last in fairy lights: Quality of batteries

The quality of battery used in the fairy lights is another factor that will determine whether your fairy lights last through the night or just half of it.

Cheaper batteries are manufactured to cut down on overall cost with the end game of making more profit. 

This comes at another cost however of cheaper materials being used. This greatly reduces the overall performance of the battery which will be evident when your fairy lights turn prematurely. 

So, check the stock battery that comes with your fairy light and make sure it is a good quality, reputable brand. 

Factor #5 of how long batteries last in fairy lights: How long it is left on for

Finally, on the list of factors of how long batteries will last in fairy light, is how long you leave them on for.

This might seem like a no brainer, but it’s worth noting. 

If the fairy light is turned off after a short period of time, this going to mean that the battery will last for longer than just keeping it on when not needed.

Turning them off when not needed can extend the battery’s life for weeks.

How long do the standard batteries last in fairy lights?

As there are different fairy lights as well as batteries, knowing exactly how long a battery will last in your particular case will be hard. 

But, we can make a rough estimate of the standard batteries as well as LEDs used. 

As the length of a fairy light increases, the voltage needs to increase as well to supply the LEDs with enough current to turn them on. 

So, the longer the fairy light, the more batteries are required. 

Coin Cells (CR2032) are the common type of battery used to power fairy lights due to their sleek design. This means the battery case can be smaller making the overall setup easier to manage. 

CR2032’s are the standard brand supplied when you buy most fairy lights (if any batteries are supplied). So, I will use them for my calculations.

They have a nominal voltage of 3V and battery capacity of 250mAh.

The table below summarizes the rough estimates of how batteries will last for different lengths of fairy lights.

Again, these are all just estimates for an ideal situation. There are many variables that will affect these values.

Note, when you double the voltage of a battery (by connecting it in series), it’s battery capacity remains the same. This is why for lengths 3-5m, the number of hours decreases. 

To increase the battery capacity using two batteries, you will have to connect them in parallel. 

How to make fairy light last longer using batteries

Fairy lights are designed to be operated by batteries since they are used in applications like temporary decoration setups in weddings, parties, etc.

So, plugging them into a power outlet isn’t an option to make them last longer. 

But, fear not! There are a couple of things you can do to extend the life of your fairy lights. 

Tip #1 making batteries last longer in fairy lights: Turn them off

The first tip is the simplest so I thought I’d get it out the way and is to turn the fairy lights off.

If you do not require to run them for long periods of time, turn them off. This could extend the batteries for weeks on end! 

Tip #2 making batteries last longer in fairy lights: Use higher capacity batteries

As you now know, the higher the battery capacity, the longer that your batteries will last in fairy lights. 

The stock batteries supplied with the fairy lights might not have sufficient battery capacity, so you might have to replace them with ones with higher battery capacity. 

Remember to invest in good quality batteries as well. 

Tip #3 making batteries last longer in fairy lights: Opt for smaller LED fairy lights

There are many different styles of fairy lights available for many different occasions. 

The type of light, as well as size is going to vary. 

If you need your fairy lights to last for long amounts of time, opt for ones that use smaller sized LEDs as they will consume less current. 

Also, if you only require 3m of fairy light, do not buy one that is 5m in length. 

Benefits of using rechargeable batteries for fairy lights

You can only extend the life of batteries so much before you will have to throw them in the bin. 

Using disposable batteries is not only harmful to the environment, but is a waste of money.

Rechargeable batteries, as the name suggests, are batteries that can be recharged and used again and again.

This means that you can reuse them with your fairy lights without having to throw them out which is going to be beneficial for the environment and your bank account.

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