Specifications

8.4. BATTERY SELECTION AND CHARGING
determined based on the open circuit (or very light load) potential difference.
This relationship is not linear, however and the measurements are temperature
dependant. Higher temperatures give higher potentials for the same state of
charge (SOC). Lower temperatures result in lower voltage readings and a
decreased storage capacity [23]. At 0
◦
C, only 85% of the battery’s rated
capacity is available [24]. Figure 8.3 shows the battery’s state of charge for
given open circuit voltages at 25
◦
C. Although this relationship is non-linear,
the temperature-SOC relationship is approximately linear and the interaction
of these two variables can be linearly approximated as
SOC = 92V
oc
− 14T − 750,
where V
oc
is the open-circuit voltage and T is the temperature in
◦
C.
Figure 8.3: Battery SOC vs Open circuit voltage.
Showing actual SOC and estimated SOC at 25
◦
C. Data from [23] and [25].
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