What’s the difference between all the different battery sizes? Why do some need AA and others AAA?



What’s the difference between all the different battery sizes? Why do some need AA and others AAA?

In: Technology

Most of the round ones are the same, the only difference is the amount of energy they can provide and the physical size. Sometimes you prefer more capacity even though it will take more space and vice versa.


Smaller batteries have the same voltage (1.5v) but it might be worth it to fit them into smaller devices.

They are just different sizes. AAs hold more power so they last longer, and offer a better value, if you have room for them. AAAs are smaller, so if you don’t have enough space to hold AAs, you can use AAAs instead.

Most common batteries such as AAs and AAAs have the same voltage, about 1.5v each. If you need more voltage than this, you may need to add multiple batteries together. 3x AAAs could give you 4.5v for example (when fully charged) so if your device requires 4.5v, you need at least that many.

They are still just different sizes, though. If you need 3 batteries minimum due to a voltage requirement, you may use 3x AAAs because this is small. But if you wanted the device to run longer and need replacement less often, you could design it to hold 3x AAs instead. The only issue is, AAs are larger (they are also more expensive to buy, so if a company is including batteries they may want to use smaller ones, but it saves the user money in the long term by not requiring replacement as often)

From a historical perspective, batteries didn’t store energy very densely, so they needed to be physically large in order to have any kind of a useful battery life. Also, physically large batteries could deliver more energy faster than smaller ones, so something like a flashlight would be dimmer with physically smaller batteries — even if you were okay with the shorter battery life.

So, D cells were common for things like flashlights and boom boxes because they needed to be big to handle the power drain. But as battery chemistry improved, we could make C cells perform pretty well, and as a side benefit, our flashlights could be smaller and our boom boxes lighter. As batteries continued to get even better, we could reasonably power devices with AA and that opened up opportunities for smaller portable devices, like Sony Walkmen. Same goes for AAA — even more devices and smaller devices like TV remote controls.

It didn’t really happen that way exactly, but the idea is you use the physically smallest battery you can depending on how much power and battery life you need for your device. So today, something like an airbed inflator might use D or C cells so inflate a mattress more quickly and more times than AA cells could.

In the main, batteries differ in capacity (amps/milliamps) and electric potential (volts). You can think of electricity as being kindof like water, and a battery as being kindof like a squeeze bottle of water. Capacity, then, measures how much water your bottle holds, in milliamps. Voltage tells you how forcefully the water shoots out of the bottle.

With more milliamps, your battery will last longer. With higher voltage, your battery can be used to achieve more powerful effects, faster. For instance, you can’t start your car engine with 1.5 volts. You need to deliver 12 or more volts to move the starter and ignite the fuel.

AAA and AA and D batteries all deliver the same 1.5 volts. AA and D batteries are simply larger, having higher capacity in milliamps than a AAA battery has. You can, for instance, use AA batteries in place of a D if you have a round adapter for that and it will deliver the same 1.5 volts.

Your rectangular 9-volt battery puts out (surprise) 9 volts, but only holds like 600 milliamps, so it won’t last as long as a AA.

That’s the basics. Next step is understanding that you can put multiple batteries in parallel (for same voltage, more amps) or series (for same amperage, more voltage). In fact, sometimes you can crack open a large battery and inside will just be a bunch of smaller batteries wired together.