Inside a 9-Volt Battery
In the bottom photo, you can see that all six AAAA cells are connected in series. Each individual cell is 1.5 volts,
so 6 x 1.5 = 9.0 volts.
For a size comparison, a standard triple-A (AAA) cell is shown next to one of the AAAA cells.
Here are the specifications for the Duracell Ultra 9V battery:
Battery Capacity: 550 mAh
Battery Technology: Alkaline (Single Use)
Current: 2.1000 A
Depth: 17.0 mm
Height: 48.5 mm
Voltage: 9.00 V
Weight: 44.0 g
Since the cells are connected in series, than means the overall current rating for the battery assembly is the same for each AAAA cell. So, each AAAA cell is rated at 2.1 amps with an energy capacity of 550 mAh (milliamp-hours).
Prior to the advent of miniature wireless devices like Bluetooth headsets, wireless mice, stereo remote controls, etc., almost nobody had ever even seen a AAAA cell. Still, probably the vast majority of people do not know that the familiar, ubiquitous 9V battery is composed of six of them.
Now you know.