Solar lights are a popular way of adding lighting to a garden or other area around the home to help guide people or to act as a security feature. The great thing about them is they use energy from the sun, so not only does that mean you don’t have to have wires all over your garden, stretching to the nearest plug socket, but they are better for the environment too. But that environmental benefit would soon disappear if you bought new lights every time the batteries ran out, so, for this reason, you may ask how do you replace the batteries in solar lights?

The short answer is that in most solar garden lights you can simply remove the battery cover, take out the old batteries which came fitted with the device, and replace the battery with a new rechargeable battery of the same specification.

But which type of battery do you need? Are there any other special steps you must take? Well in this article I will explain this in depth.

 

Why do solar lights need batteries?

 

You may be thinking, why do my solar lights even need batteries? I thought the whole point was that they used the suns energy rather than that for a battery?

Well, the problem is that the sun is only providing energy for the small solar panel on your lights to generate electricity in the day time. So if you only needed your lights to work in the day time you wouldn’t need a battery because the energy could be converted instantly. But you may have noticed the problem here, solar lights aren’t much use to us if they are only on in the day time, we already have the suns light doing that job for us. We need a way to store this energy so it can be used when we really do need it, when it’s dark.

Solar lights therefore come fitted with a rechargeable battery, which can store energy from the sun in the day time and then hold on to it until night time when it is used to power the lights.

Rechargeable batteries are everywhere these days, in pretty much all our electronics from smartphones to cameras.

 

What are the different types of rechargeable battery?

 

There are a number of different types of rechargeable battery available now. These vary as technology has improved and also in cost to manufacture. So a higher end solar light may have a more expensive type of battery than a cheaper solar garden light, which will have a cheaper model.

The battery has to contain an element that loses electrons easily. These electrons are what pass back and forth between two sides of the battery to store and release a charge and to produce electricity.

 

Lithium-based batteries

 

Many larger, modern solar lights now contain lithium-based batteries. These are the same as those found within your smartphone or laptop.

They are used as they can have an energy density over twice that of older style nickel-based batteries (which I will talk about later).

The other advantage they have over the older battery models is that you can get a 3.6volt battery pack as just a single cell rather than having to have a number of smaller cells (typically 1.2 volts) joined in a series. This saves a lot of space which is a bonus in solar lights where you don’t want to have lots of small batteries packed in next to each other.

 

Nickel -based batteries

 

In cheaper solar garden lights the batteries are most likely to be Nickel based. This could be either Nickel Cadmium (NiCd) or Nickel Metal Hydride (NmH).

This type of rechargeable battery has been around for a long time. The first Nickel Cadmium battery being created way back in 1899!

Nickel Cadmium batteries are becoming less common these days and have been replaced by Nickel Metal Hydride batteries in most cases, so the later is what you are probably going to find in your solar garden lights.

There are a few reasons for this, they have a higher capacity, are now more cost-effective, and (most importantly for this blog) are much better for the environment. Cadmium is a highly toxic element, toxic to all forms of life. So if not disposed of correctly these can have big implications for the environment.

Cadmium-based batteries do still appear though. They still have a couple of advantages for manufacturers in that they have a higher maximum discharge rate and so can provide more power when needed. Secondly, they have a lower ‘self-discharge’ rate. This is the rate at which they lose charge simply by being left. But we think that those small advantages are outweighed by the environmental disadvantages and you should avoid these batteries if possible.

 

Can I replace Nickel Cadmium with Nickel Metal Hydride?

 

Ok so I’ve been saying you should ditch the cadmium batteries and use metal hydride instead, but if your solar lights came with cadmium-based batteries already installed can you replace them with metal hydride ones?

Well yes you can, a solar light should still work in just the same way if you change to this battery type providing you get matching specifications in other areas, i.e the size and voltage.

The one thing to bear in mind is to not mix the two types. So say you open up your solar lights and find there are two batteries inside, but maybe you want to try just replacing one to see if the other is still holding charge. Don’t do this.

Always replace all the batteries so you have just one type of battery in your solar lights.

 

Can I replace Nickel Cadmium with a Lithium-Ion battery?

 

This is technically possible but I wouldn’t recommend it. You will probably have to adapt the connection type and fiddle with the electronics to make it work in the first place and once you have done this you may come across issues as Lithium batteries have a high discharge voltage and may cause damage to the LED in you lights.

 

Can I use standard alkaline non-rechargeable batteries in a solar light?

 

No. It is very important that you do not try and use regular alkaline non-rechargeable batteries in your solar lights. You may be tempted to do this as you might have some spare batteries lying around the house, but the solar light assumes you are using a rechargeable battery and so will try and recharge the alkaline battery.

Technically the batteries can recharge but what is quite likely to happen is that it will cause gas to be released in the reaction which will build up inside the battery casing and then……explode. This will probably ruin your solar lights, and if not will leave you with a hell of a mess to clean up!

 

What type of battery does my solar light contain?

 

The best way to find out is to check the leaflet that came with your lights, or if you have lost this check on the manufacturers’ website.

On Amazon, for example, if you scroll down on any solar light page to the specifications section, you will see a ‘battery type’ specification. This may say something along the lines of:

“18650 lithium battery 3.7V 2200mAh” or

“1.2V 150mAh AA Ni-MH”

 

What does the mAh mean?

 

This abbreviation which you will see alongside most rechargeable batteries stands for “milli ampere-hours” and is a measure of current and in basic terms tell you how long the battery will last when fully charged.

 

Will my lights last longer or be brighter if I use a higher mAh value battery?

 

I have already mentioned trying to replace your battery with one of the same specifications if possible. But could upping the specs improve the performance?

Well, unfortunately, this is not likely. The length of time your lights stay on for is determined by the amount of sunlight that gets to them during the day. If a light is supplied with a 900mAh battery the manufacturer has hopefully tested that and knows it is high enough to store enough energy to last through the night. So even if you replace this with a 2000mAh battery for example, the battery can only store as much energy as it receives from the sun each day and so the higher capacity won’t actually have any benefit, it will just cost you more money!

So yes, a higher mAh value will give you longer battery life for each charge, but whether you will see the benefit is questionable. By all means, give it a go though.

 

Instructions on how to replace a solar light battery

 

 Step 1: Take your solar light indoors to a clean dry space

 

You don’t want to get any water or dirt in your solar light that could affect future performance. For this reason, take your solar light indoors to a nice clean area before opening it up.

 

 

Step 2: Unscrew the top of the light

 

In the vast majority of cases with solar garden lights, the solar panel and battery are housed in the very top section above the bulb. In my solar light used in the example here you simply twist the top section about half a turn anti-clockwise and it comes away

             

Step 3: Switch the light off if there is the option to

 

If you have the option, to be extra safe, turn the light switch to off before touching the battery.

 

 

Step 4: Open the battery casing and see what type of battery you have

 

As you can see in my example here, the solar light is powered by a simple 300mAh, AA, 1.2V Nickel Cadmium battery. You may notice sometimes it says ‘no mercury’ on the casing. This is simply to let you know that it can be taken to a battery recycling centre which will often state ‘no mercury allowed’.

 

 

Step 5: Remove the battery

 

Step 6: Find a new battery of the same specification or similar

As stated earlier in the article it is recommended you use a Nickel Metal Hydride battery to replace a Nickel Cadmium battery as they are better for the environment.

 

 

Step 7: Turn the light back on and test 

There is a good chance your new battery will come charged so turn the light back on a test it by covering the top. If nothing happens the battery may not be charged yet so leave it in the sun for a few hours before testing again.

 

 

How to dispose of used batteries 

 

 Do not simply throw your used batteries in the nearest bin! These will then end up in landfill and the toxic cadmium will likely leak out into the environme

Take your batteries to your nearest recycling centre. In the US click here to find a center near you. If not many stores such as Home Depot, Best Buy and other similar electronic and hardware stores will have battery recycling points.

 

 

Rob Wreglesworth

Rob is the head writer and podcast producer for The Disruptive Environmentalist. He is on a mission to build a community of people that are passionate about solving environmental problems.
Rob Wreglesworth
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