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
You mean like a CR2 and the CR123A battery ?
They exist, but the mass production of AA and AAA batteries makes them a lot cheaper, and can be found in almost every shop in the world.
Also, using two AA batteries can be more versatile as they can be be used in serial making 3V or in parallel making double the energy in 1.5V
Why bother when an extremely simple solution already exists?
Just to blow your mind, a 9 volt battery has 6 AAAAs wired in series. A 6 volt lantern battery has 4 D cells.
Electrical engineer here, there are many reasons for this:
1. While many devices need 3.3v (usual voltage from two 3.3v cells), many more need 5v, 12v, 9v, or some other voltage; rather than having to make a large number of batteries in different voltages, it’s easier to simply standardize the batteries and use more or less of them
2. Some devices need a positive, negative, and neutral voltage to work properly. Having two or four alkaline cells with a tap in the middle is an easy way to accomplish this
3. Multiple smaller cells gives you a bit more flexibility in allocating space and weight for power storage — having a giant brick that can’t be broken up into smaller bits is gonna make life a lot harder during board design.
4. The options for raising the voltage coming out of a battery are to combine a bunch of small cells (more expensive and reduces power capacity), add a switching DC-to-DC converter (more expensive, can add some nasty ripple voltages if you don’t cram in even more electronics, those extra electronics also reduce capacity, and disposing of the battery becomes much harder), use a chemistry that naturally ouputs a higher voltage (even more expensive, and you’re not gonna get that much more out of it), or use something that isn’t actually a battery such as a fuel cell or radioisotope generator (ridiculously, heart-stoppingly expensive, dangerous, hard to source, possibly illegal, and damn-near impossible to get safety certifications for). It makes more sense just to get multiple cells and do any voltage conversion onboard the device.
5. If a single cell turns out to be faulty, it’s cheap to replace; if a cell in a battery fails, it costs more to replace and it’s harder to diagnose
There are already [plenty of standards](https://en.wikipedia.org/wiki/List_of_battery_sizes), with different sizes, voltages, capacities, and form factors. Another standard isn’t needed. But most of those standards aren’t often used. Because it’s easier and better for everyone to just stick to the most commonly available and interchangeable ones.
Batteries are modular. If you wire them in series, their voltage “stacks”. If you wire them in parallel, their capacity stacks. Because alkaline batteries produce around 1.5V per cell, you can design your device to work with any multiple of 1.5V, then just wire up alkaline batteries (of any size) in series and get the voltage you need.
However, as you’ve noticed, not many devices rely on only 1.5V. Most work with 3.0V or more. Alkaline battery chemistry only produces 1.5V per “cell” though, and a single alkaline battery typically only contains a single cell. Packaging more than one cell together increases cost, so it’s cheaper to simply require two separate batteries.
There is one type of alkaline battery that combines more than one cell though; the 9V battery. Many 9V batteries are actually six AAAA — yes, four-A, which isn’t a size you see often — batteries packaged up as a brick. More modern 9V batteries use something called pancake cells stacked up like sandwiches though. They made the switch because you can get more capacity in a single 9V battery this way, because it uses up more of the space. Since consumers prefer batteries with more capacity, this pushed the industry to move away from the 6 AAAA battery packaging.
Lots of things made for AA can run on AAAs with tin foil. I think it has more to do with manufacturers
For the weird case where you need 4.5V (aka 3 batteries). It creates a unit that you can build “standard” / cookie-cutter circuits from.
So that the battery industry can keep making money off the consumer by over charging for batteries.
Some penlights only need 1 battery, other devices need 2,3,4 or more. You could create one battery that’s equivalent to 2, another that’s equivalent to 3, and so on, but it’s more flexible to have one standardized battery that works in all configurations.
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