From Unofficial Zero Manual
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Battery capacity is a measure of the charge a battery can deliver at an intended voltage.

Cells themselves are usually rated for a current amount delivered over an interval of time (going from maximum voltage to a rated minimum).
Batteries as banks of cells aggregate that measure across the cells.
Because of a number of factors including internal resistance, a higher discharge rate effectively lowers the usable capacity of the battery during that cycle.
This variance in the usable capacity of the battery has meaning for how an electric motorcycle performs with different riding styles.

Normally, the energy a battery can store is estimated by taking nominal voltage (V) times the current capacity of the battery's cells (Ah) = the energy delivery capacity (Wh) (divide by 1000 for kWh).

PackVoltagenominal (V) × CellCapacity (Ah) = EnergyCapacity (Wh)

However, based on industry convention, Zero calculates battery energy (the kWh) by taking the maximum voltage the battery has at 100% capacity times the capacity in Ah, instead of nominal voltage.

Maximum Voltage
Maximum voltage is only present at the beginning of discharge when it is full, and then it drops (nonlinearly).
Nominal Voltage
The nominal voltage is like the average voltage the battery over the entire discharge range.
The average is the voltage measured at the battery terminal when it has 50% charge state and is disconnected from any load.

For example, the 2013 S has 100Ah and a nominal 102V: the total energy the battery has is:

102V × 100Ah = 10200Wh = 10.2kWh

But if you use maximum battery voltage you get:

116V × 100Ah = 11600Wh = 11.6kWh

This also applies when adding a power tank, confusing customers about the official rating versus what the mobile application reports.

Regardless of this complexity of measurement, Zero's range figures appear reliable in the general context of the test conditions.