A23, 8LR932, 1811A, V23GA, MN21, 8LR23, A23S Battery Equivalents and Replacements
According to IEC standard, this battery label is 8LR932 and according to ANSI standard its label is 1811A.
However, A23 battery is also commonly known as V23GA, MN21, 8LR23, A23S, 23A, 23AE, L1028 etc.
A23 battery dimensions are 10.3 mm in diameter and 28.5 in length and it weighs around 0.3 oz (8 grams).
Internally, A23 battery consists of 8 alkaline LR932 batteries connected in series - hence the label according to IEC standard of 8LR932.
LR932 battery itself is alkaline battery, 9.3 mm in diameter and 3.2 mm in height, with nominal voltage of 1.5 volts and cut-off voltage of 1.0 volts. LR932 battery is almost never used as a single battery.
Thus, A23 battery nominal voltage is 12.0 volts, cut-off voltage is 6.0 volts and nominal capacity is in the 50-60 mAh range.
Capacity also depends on discharge current, for example Energizer A23 battery nominal capacity is 55 mAh, measured using 22 kΩ resistor at 21°C down to 6.0 volts.
Higher discharge currents lead to capacity drop, for example, at 5 mAh, capacity drops down to ~43 mAh, at 10 mAh down to ~30 mAh, at 15 mAh down to ~26 mAh, etc.
Since LR932 are alkaline batteries, A23 battery voltage also drops over time and when the voltage drops down to 6.0 volts, battery is considered to be fully discharged.
Note: Temperature also influence voltage, especially when the battery is in use for longer period of time. If you are facing issues with 'almost dead' battery due to freezing temperature, and need your battery for 'just one more click', try to warm it in your armpits for few minutes - voltage might increase above required threshold for the device you are having - and change the battery as soon as possible!
For Short: A23 battery is easily found at local hardware shops, online stores and similar places. Since they have good shelf life (3-5 years, sometimes even more), and are rather cheap, having few of them stored is not a big expense.