Xantrex Technology LINK 10 - Manual (Page 46)

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Electric Vehicles (EVs)
The Link 10 is the ideal energy meter for EV instrumentation. It not only
provides volts, amps, amp hours and time remaining, it adds two important
bonuses: kilowatt hours and optional serial computer output.
If you design or work with electric vehicles or battery-powered equipment
of any type, you should realize that kilowatt hours are a more accurate
measure of energy used than are amp hours. Here's why:
The term "amp hour" defines current (amps) multiplied by time (hours).
Amp hours is one way to state battery capacity. Amp hours is not a measure
of energy consumed by a vehicle. Energy is defined as:
Energy in watt hours = voltage x amperage x time.
Consider two examples: First, assume we have a 120-volt battery that
supplies a 100-amp load for 1 hour. At the end of one hour, 12,000 watt-
hours (12.00 kWh) will have been consumed. In the same period of time,
100 amp hours will be used.
But now suppose we have a 240-volt battery supplying a 100-amp load
for one hour. What happens to the math? Well, 24,000 watt hours (24.00
kWh) of power have been consumed. The amp hours consumed is the
same as the first example, 100 amp hours, but twice the energy has been
consumed!
That's why electric vehicle efficiency is judged on kilowatt hours. A kilo-
watt hour is a 1,000-watt load for a period of one hour. You buy kilowatt
hours from the power company (to keep the lights on in your home) at a
typical cost of $0.05 to $0.15 per kWh. By comparing the cost of kilowatt
hours from the electric company with kilowatt-hour consumption of an
electric vehicle, you can accurately judge EV operating costs.
Refer to the Owner's Manual for instructions on use of the kWh display.