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3. Battery capacity estimation
3.1. What is battery capacity
Battery capacity is an electrical charge (quantity
of electricity) that battery can deliver under specified
conditions. Usually battery capacity is expressed in
ampere-hours (A*h or Ah). Capacity equals to discharge
current (in amperes) multiplied by discharge time (in
hours). Battery producers rate nominal battery capacity
for some standard conditions. Usually (but not neces-
sary), these conditions are: 20-hour discharge time,
20
o
C discharge temperature and 1.75 V final battery
voltage (voltage limit at which discharge is considered
to be complete).
3.1.1. Dependence between battery capacity
and discharge current
Charge that a battery can deliver depends on the
discharge current (discharge time). If discharge current
grows (discharge time decreases), the battery capacity
decreases. This dependence is an individual property of
a specific battery. The dependence between relative
battery capacity and discharge time for LCL-12V33AP
battery is given in the table below.
Discharge time,
hours
Relative capacity, %
0,1
37
0,3
48
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Discharge time,
hours
Relative capacity, %
0,7
53
1,9
76
4,2
84
9,2
92
20
100
Qulon-12ns always shows capacity for 20-hour
discharge time. If you discharge your battery during
smaller time, the capacity will reduce.
3.1.2. Battery capacity and battery state of
charge
We need to distinguish capacity and state of
charge. Capacity is the quantity of electricity that a fully
charged battery can deliver. State of charge is a charac-
teristic giving information on the degree to which the ca-
pacity is filled. For example 33Ah battery can contain 33
A*h if a battery is fully charged and 10 A*h if the battery
charge is not full.
Qulon-12ns estimates capacity of fully charged
battery and can’ be used to determine state of charge.
3.1.3. Temperature dependencies
While testing battery under low or high tem-
perature, dependence of battery capacity from the tem-
perature should be taken into account. Qulon-12ns al-
ways shows the capacity that a battery could deliver
during next discharge under the same condition. That is
why if you get estimated capacity under plus 20
o
C as