Car Battery Milliamps

What do batteries with different sizes/voltages really mean?

Compare these:

1.5v AA battery.
1.5v AAA battery.

Am i correct that these are the same voltage? What advantage does one have other the other? Is it just more milliamps (mAh’s)?

Compare a huge 6 volt square battery that goes into one of those big flashlights. It says 6 volts. Why does a little battery like 1/10th of a 6 volt battery say 9 volts?

From personal experience, I’ve seen a car battery tested at around roughly 12 volts. Yet a little square 9 volt battery is “9 volts”?

Can someone explain the differences? Even a massive change in milliamps (mAh’s) would not change the voltage itself. What am I missing? Amperage or something? If that’s the case…why do we refer to it in volts if the amps are what does all of the powering moreso than the volts?
Pardon the spelling errors…it’s late.

*over the other?

A battery is a group of cells. A single cell (usually mistakenly also called battery) usually has a voltage of 1.2, 1.5, 2 volts, depending on the chemicals used. Most non-rechargeable ones are 1.5 volts.

You are correct, there are different cells with the same voltage, 1.5 volts. That is because there is more material used, so they will last longer, and can supply more current. A 1.5 volt cell comes in lots of different sizes, from one the size of a dime to a D cell for a flashlight. And these have storage capabilities ranging from 100 mA-hour to 12000 mA-hr.

Now you can combine a bunch of cells to make a battery. The common 9 volt battery has 6 small cells in it, so although it has a lot of volts, it has little storage or current.

Also note, you can combine cells or batteries in parallel, where the voltage remains the same, and the capacity and current capability increases.

A lantern 6 volt battery has 8 large D size cells connected series/parallel in it to make the 6 volts, and it can supply a lot of current for a long time.

Auto batteries are commonly called “lead acid” because of their construction. they produce about 2 volts per cell, and the battery has 6 cells for 12 volts. Because the cells are large, the battery can supply hundreds of amps, a lot of power.

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Whats a UPS?