We have received many inquiries regarding the various sizes of rechargeable batteries for solar lights. There are a few reasons why manufacturers choose one size over the other. They are as follows:

1. Compact size means a smaller battery compartment and overall smaller solar light for the customer.
2. Chemistry choice will determine the Voltage output for like-sized batteries.
3. Commonly used battery sizes on the market will reduce the production costs and final price for the customer.
4. Chemistry choice will affect the environmental impact of the battery once its life cycle has terminated.

So, we will address each of these points above in further detail.

Item 1. A smaller battery will give the manufacturer the option to create a solar light that is smaller than what it would be had a larger rechargeable battery been used. Smaller batteries can store the same amount of energy capacity (mAh, or milliAmp hours) for each night’s use. For instance, a 600 mAh 1.2 Volt rechargeable battery can come in either a AA or AAA size.  However, if you compare it to water flowing in a river, the AAA size is going to be a smaller river width, while AA batteries represent a larger river and thus more water can flow through.  They will both flow for the same amount of time, only the AA will be able to provide more current (water, in our river example above) than its AAA counterpart over the same amount of time.  The force of the water (ie: Voltage) is the same for both, only the AA will be able to provide more current and thus, a larger or demanding LED component (think, more current will allow for a brighter LED to be used). In the image above, two Lithium batteries with the same specifications are set side by side. However, the black battery is what is considered a 2/3 AA, while the grey battery is the more common AA size. The smaller battery will give the same output, but for a less powerful LED demand. The smaller battery is compact, but it is sufficient enough for a lower output illumination device (in this case, it was used in a solar spot light with 1 LED that was purchased from a big box store.) The advantage of the smaller battery is that it allows for a smaller solar light. The biggest disadvantage is that the replacements for these batteries are difficult to find, and when found, relatively expensive compared to their AA counterparts.

Item 2. The battery chemistry will play a factor in the design in a number of different ways. For one, the amount of electrical potential (Voltage) that a battery can provide will depend on the chemical makeup of the battery. AA Lithium ion batteries typically have a Voltage rating of 3.2 Volts; whereas the same size NiMH (Nickel Metal Hydride) or NiCd (Nickel Cadmium) will have a Voltage rating of 1.2 Volts.  So, using a Lithium battery in a NiMH light will burn out the LEDs of the NiMH light almost instantly. The LED will be brighter than ever, but that moment in the spot light, so to speak, will end in a matter of seconds. So it is recommended to not use Lithium batteries in either NiMH or NiCd battery lights. Using a Lithium battery will give the manufacturer the option of increasing the LED load capacity (thus a brighter light), but will ultimately cost the customer more in the long run as replacement batteries for Lithium lights are more expensive.

Item 3. Since AA and AAA battery sizes are more common (AA moreso than AAA) than fractional sizes (such as the 2/3 AA in the photo above), costs for production have been set to allow for the best available pricing for customers worldwide. Being that AA batteries have been around since 1907, their production infrastructure has had plenty of time to develop and take hold on the battery market. There are square 9 Volt and larger Lead Acid rechargeable batteries on the market for use in solar lights. However, since they are odd shaped for the purpose of streamlining solar light designs, they are less commonly used and ultimately will cost more (also for the fact that they hold more energy) and are weighty.

Item 4. There are a number of chemical components that make up solar light rechargeable batteries. The primary distinguishing components are Nickel Cadmium (NiCd), Nickel Metal Hydride (NiMH), Lithium Ion and Lead Acid.  Developed in 1899 by Swedish inventor Waldemar Jungner, it would take NiCd batteries over 4 decades to hit the market for commercial consumption. At the time, the competitor for NiCd batteries was the Lead Acid battery. However, due to the latter’s dimension restrictions as a small and portable battery, NiCd took hold and was widely used as a consumer-ready battery. Not until 1989 (with subsequent years of development) was the NiMH battery introduced to the market as an alternative to its Cadmium-based battery. NiMH rechargeables are capable of a better performance over the long term (for solar garden lights, typical lifespan of both chemistries is about 2 years). NiMH rechargeables also use a mild toxicity chemistry as opposed to the heavy metal toxicity of Cadmium (which makes up about 18% of the battery). NiMH batteries are capable (although it is recommended to recycle them whenever possible) of being thrown out in the trash. Whereas NiCd batteries must be recycled/disposed of in the proper facility. Lithium Ion batteries are taking their hold on the market due to their unsurpassed performance compared to other chemistries. But their setbacks are their disposal at the end of their lifecycle (recycling costs more than mining, so they may likely be thrown in the trash), higher cost of the battery for the consumer and transportation restrictions.

So, with all the considerations above, you will be better able to find the right solar light for your specific project. All of the battery chemistries have proven to have working track records, but each have their own pros and cons. Just be sure that the specifications you are looking for match what your solar lights came with when you first purchased them. If you are still not sure about the correct solar light batteries to use, check out our previous posts on the subject. There is much to know, but it is all worthwhile as solar lighting has great potential when it comes to illuminating your home, garden and office exteriors.

Should you have any questions or like to have us discuss other aspects of solar lighting around your home, send us an email at info@yoursolarlink.com. Be safe and stay solar!

Mario @ Your Solar Link