What is the difference between using multiple 1.5V batteries and one 9V battery?

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I had a toy when I was a kid that took 6 AA batteries. Now I know that means it wanted around a 9V input. But why did it take 6AAs instead of one 9V? The 9V would’ve been smaller and lighter, wouldn’t that have let them make a smaller battery compartment and save on manufacturing costs?

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Voltage is just one requirement. Amperage requirement is another. The larger cells of multiple batteries is able to provide more Amperage and will also usually last much longer. Typical requirement of kids toys.

>I had a toy when I was a kid that took 6 AA batteries. Now I know that means it wanted around a 9V input. But why did it take 6AAs instead of one 9V? The 9V would’ve been smaller and lighter, wouldn’t that have let them make a smaller battery compartment and save on manufacturing costs?

A 9V battery usually **is** a stack of 1.5V cells. There is no difference, with the obvious caveat that 6AAs will have a significantly larger combined capacity than a 9V block.

The classical square 9V battery shape is actually made up of 6 smaller round cells. However the smaller batteries can not provide as much current as the larger batteries and will also go flat sooner. So for example a boom box would usually require D cell batteries as it needed lots of power to run the amplifiers and speakers.

>The 9V would’ve been smaller and lighter, wouldn’t that have let them make a smaller battery compartment and save on manufacturing costs?

The 9V is only good for high voltage low current applications, it won’t last long if you start pulling a sizable amount of current from it

A 9V battery is effectively 6 AAAA cells in a package, they’re really skinny batteries and can’t provide much current. A 9V only has a capacity of around 560 mAh compared to a standard AA battery at 2700 mAh so 6 AA batteries will last around 5x longer than a 9V under low load and significantly longer under higher loads.

This is the same reason that flashlights use C or D cells instead of just AA batteries in series, the AA cells cannot support the power draw for very long and will die much quicker than you’d expect

This is the same sort of question as asking why a boombox needs five D cells, and not just five little button coin cells. Both are 1.5v per cell, so what’s the difference?

The difference is ability to supply current, and capacity.

The bigger the batteries, the more power they can deal out, put simply.

9V batteries kinda suck for that. They’re just used in applications where 9V is necessary for the electronics, but those electronics don’t actually use much power.

Voltage is only one characteristic of a power supply.

Two other really important ones are max current (how hard it has to work to turn the wheels) and energy storage (how long it can last before you need to replenish it).

9V battery has relatively small max current and energy storage. It’s mainly for low-power applications.

A toy probably has higher power requirements and also needs to last longer between battery changes.

It may not have wanted 9V, it could have been 4.5V.

In that case the batteries would be wired in parallel to provide double the current, but half the voltage.

I would also guess that 6 AA batteries have a higher capacity than a single 9V battery, meaning it lasts longer.

Its also worth considering lazy development/cheap manufacturing. It wouldn’t be too surprising if the connections for AA were cheaper or the manufacturer happened to have bought them for something else, or they reused an old plastic mold from a different toy to save money.
I think that some sizes of batteries are even just more commonly used in different parts of the world, so maybe it was designed where AA batteries were super common.

A 9V battery is just six tiny 1.5V batteries in a package, [like here](https://softsolder.com/2009/01/08/inside-9v-batteries/). It’s just for your convenience, not having to deal with a bunch of essentially AAAA batteries.

But those are very tiny batteries so they each don’t hold much a charge. You’ll get a LOT more battery life from six AA batteries than a 9V.