A few common terminologies related to batteries.
Nominal Voltage – The voltage that is marked on the cell is called nominal voltage. The nominal voltage is different from the actual operating voltage. It is important to note that the actual operating voltage can be higher or lower than the nominal voltage. The use of the nominal voltage is that it helps the user match-up equipment. For ex: A 12 volt nominal battery can be matched with a 12-volt nominal charge controller.
Capacity – The capacity of a cell is represented in ampere-hours (Ah). The nominal capacity of a cell is also marked on the battery. When a cell is marked with 2000 mAh, it means that one can draw 2000 mA of current from the cell for one hour or 1000 mA of current for 2 hours.
Total Energy Storage Capacity – The total energy storage capacity of a cell is roughly its nominal voltage multiplied by its nominal capacity. The unit is Wh. Another common term, Specific energy defines the battery’s energy storage capacity in terms of weight (Wh/kg)
C-rating – The C-rate specifies the rate at which a battery is charged or discharged. At 1C, the battery charges and discharges at a current that is on par with the marked Ah rating. At 0.5C, the current is half and the time is doubled. For ex: A 20 Ah cell will deliver 20 A for 1 hour at 1C rate or 10 A for about 2 hours at C/2 rate (but the relationship is not strictly linear).
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