The difference between AA and 18650 batteries

For those of you of a certain vintage (basically circa the grand old age of 30), if you’re anything like us you’ll remember the days of packing a full box of 12 AA batteries ready to power your Gameboy Colour for the entire journey to Cornwall (and the subsequent two weeks stuck in a caravan as it tipped it down with rain). That was our annual summer holiday and every year we’d fully expect to go from Pokemon Newbie to Master Trainer within that time. Good memories.

Years later, our sole concern with batteries isn’t whether they’re giving us enough power to capture Mewtwo but the fact that they are the lifeblood of Fogstar. It also means we field questions from new customers with little to no experience on the regular - what is the difference between 18650 and AA batteries? Let’s take a look.

Voltage

First, the amount of power you can get out of either is substantially different. Typically, a Nickel-Cadmium (NiCD) or Nickel-Metal Hydride (NiMD) AA battery tends to have a nominal voltage of around 1.5V. Compare that to 18650 batteries that have a nominal voltage of 3.6V and you’ll see they’re in different leagues. To put that into perspective, to get the same voltage as one 18650, you’d need the equivalent of 2.5 AA batteries attached end to end (okay, we know, obviously it’s not possible to have half a battery, but you get our gist).

Size

We’ll let you in on a little, well-known industry secret here - cylindrical lithium batteries are actually named by their size. Take an 18650 battery for example. The “18” references the diameter of the battery in millimeters whilst the 65 covers the length (65mm). Of course, you can leave a little bit for manufacturing tolerance but in general they are there or thereabouts.

AA batteries, on the other hand, tend to be around 14.5mm in diameter and circa 50.5mm in length. Remember your Gameboy Colour or TV remote, when you’d put the AA batteries into a spring loaded compartment? Well because of this, the tolerance is much wider meaning the difference of a couple of millimetres will make no difference.

Capacity & Current

Typically, a standard AA alkaline or NiMH battery has a capacity of between 2000 to 3000 mAh. Okay, so this isn’t drastically different from an 18650 battery such as, for example, the Molicel P26A at 2600mAh. However, it’s the current where there is a real difference. Whereas the highest current drawn from an AA battery is only a few amps, there are a number of 18650 batteries that can be discharged at an incredible 8-10 times the rate of their AA cousins.

Energy Density

First of all, what is Energy Density? Well, according to the Battery University, Energy Density is, “a measure of how much energy a battery can hold. The higher the energy density, the longer the runtime will be.” We can work this out by calculating a battery’s watt hours with a simple equation. How do we do this? Take the mAh rating, multiply it by the nominal voltage and then divide it by 1000.

Let’s look at two practical examples. First of all, your standard Duracell AA Alkaline battery you’ll pick up from a reputable shop. Typically, this battery has an mAh rating of circa 1500. As you can see from the official Duracell specification sheet, it’s nominal voltage is 1.5V. Multiply the 1500 mAh rating via the 1.5V to get 2,250. Divide it by 1000 and you’ll get a result of 2.25Wh. Hardly a lot is it?

Now let’s compare it to the Molicel P26A, which has an mAh of 2600 and a nominal voltage of 3.6V. Using the same equation, we can see it has 9.36Wh. Massively better!

What this means for you

At the end of the day, it shouldn’t really be a decision for you to make. The best battery for your product is ultimately dictated by the manufacturer and we’d always recommend following their specification. After all, they know best.

Whether it’s an AA or 18650 battery, both are two contrasting products that play a critical role powering the equipment we use in our everyday lives. Without them, let’s be honest, we’d probably feel very lost! If you’re not sure about which battery to use in your product, we always recommend contacting the manufacturer or a reputable battery retailer for advice. Our team here at Fogstar will certainly do our best to help.

Now, where’s that gameboy, we were close to getting a Charizard…