ELI5. Why do most devices requiring AA or AAA batteries need at least two. Why not create a standard battery that is the equivalent of two or have common circuitry that only relies on one battery of a similar low profile?

Question

ELI5. Why do most devices requiring AA or AAA batteries need at least two. Why not create a standard battery that is the equivalent of two or have common circuitry that only relies on one battery of a similar low profile?

In: Engineering

Answer 1

The voltage of a battery is based on its chemistry. The power comes from a chemical reaction and each reaction has a certain voltage. Adding more material increases the current it can produce, and the overall power, but not the voltage. The only way to increase the voltage is to have multiple cells in a sequence, i.e. two 1.5v batteries wires from end to end are 3v (which is why they are often installed in opposite directions)

1.5v is what regular non rechargeable batteries use. Nickel metal hydride is 1.2v which allows substitution with alkaline batteries but sometimes stuff doesn’t work as well on the lower voltage. Lithium ion is around 4v.

So if you wanted to have a 3v battery standard, you’d need to either find a chemical reaction that produces 3v or you’d need to just stack two smaller 1.5v batteries in the same casing. Which adds cost and complexity to the manufacturing and doesn’t really buy you anything – if the device was big enough for multiple cells to fit, you would just use multiple cells to get the desired voltage. And there’s enough stuff out there that works with one alkaline battery or two or three that making a standard that’s, say, 3v, means you would still need to have 1.5v batteries on hand for devices that only need one cell or that need three cells (4.5v)

IMHO a much more valid complaint is devices that use AAA batteries despite having room for much larger batteries. AAs have a lot more capacity and I have a couple things around my house that are heckin chonkers that use AAA and need to be replaced far more often. The worst offender is my smart scale which is 12″ x 12″, but I also have some really big mini split remotes with screens. Low key annoyed every time I have something that clearly could have fit AAs or even larger in it and they designed it to run off AAAs