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Chapter 4: Battery Test GR8
State-of-Charge (SOC)
The State-of-Charge is one of several important factors that
aect the battery’s ability to crank an engine. It is a measure
of the available capacity remaining of a battery expressed as a
percentage of its original rated capacity.
State-of-Health (SOH)
State-of-Health is a measure of a battery’s condition relative
to a fresh battery. It is based on cranking rating, open-circuit
voltage, conductance (ability to deliver current) and battery
temperature. The tester predicts a battery’s State-of-Health
based on the characterization of Toyota, Lexus, and Scion OEM
batteries and OEM replacement batteries.
Although a State-of-Health problem can be the result of
defects in construction, most often it is a result of normal
wear-out mechanisms, which are dependant on the vehicle
needs, climate, and operating conditions. This results in
irreversible physical and chemical changes until eventually
the battery can no longer hold a charge and supply the power
necessary to start the car and provide auxiliary power to the
electrical system.
As the battery approaches end of life, deterioration accelerates,
until it nally fails to start the vehicle. Before failing, the battery
may start the vehicle under normal conditions, but may not be
able to operate in more extreme conditions. Extreme heat or
cold could expose a weak battery and cause it to fail.
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