List of common battery specifications and the meaning behind them (will be updating slowly).
If you come across any other terms, or see any mistakes in what’s listed here feel free to edit this page!
C-Rating
A battery’s capacity “decreases” when it’s discharged faster, as the internal resistance of a battery increases with discharge current, causing energy to be lost as heat.
The C-rating relates a battery’s capacity to its discharge current. Nominal capacities listed on datasheets will always have a respective standard discharge current listed as a C-rating (1C, 0.2C, etc.).
(1/#)C
# specifies how long the discharge current will take to fully discharge a battery (in hours).
1C specifies a current which will fully discharge the battery in 1 hour.
For a 1Ah capacity rated cell, this would mean a discharge current of 1A.
0.2C specifies a current which will fully discharge a battery in 5 hours (1/5).
For a 1Ah capacity rate cell, this would mean a discharge current of 0.2A.
Cell capacity ratings are always linked with a standard discharge current by the C-rating
For a 3500mAh rated battery with a standard discharge current of 0.2C:
To get a full 100% use of the 3500mAh stored you need to discharge the battery at 0.7A.
Discharging the battery at a higher current will result in lower capacity readings.
Discharging the battery at a lower current will result in higher capacity readings.
Voltage Ratings
Batteries don’t have a constant voltage. As a battery is discharged, their voltage will decrease relative to the amount of charge left in the cell, similarly to the graph below:
Nominal voltage
The average voltage that a cell outputs as it’s discharged.
Roughly equivalent to the relatively horizontal part of a discharge curve.
Max (charge) voltage
The voltage of the cell when it’s fully charged.
Typically the voltage used for constant voltage charging.
Do not charge batteries above this voltage, causes permanent damage, thermal runaway.
Cut-off voltage
The minimum allowable voltage, voltage at which the battery is considered fully drained.
Do not use batteries below this voltage, can cause permanent damage.
Battery pack voltage range
Range of voltages that a battery pack may have during operation depending its state of charge.
Maximum voltage = # cells in series * max voltage (specified for the individual cell)
Minimum voltage = # cells in series * min voltage (specified for the individual cell)
Capacity Ratings
Specifies the number of Amp-hours available when the battery is discharged at a specific discharge rate (C-rate). For example, if a battery is rated for 5Ah with a discharge rate of 0.2C, you can expect the battery to last 5 hours discharging a continuous current of 1A.
Nominal capacity
The amount of capacity the cell has if you were to discharge it at its standard discharge rate (specific C-rate).
The capacity you should expect when ordered fresh from a manufacturer.
Discharging the cell above the specified C-rate will result in a reduced capacity, and vice versa for discharging it at a lower C-rate.
Minimum capacity
The lowest capacity a cell should have when you purchase it fresh from the manufacturer
Nominal energy
The amount of energy in Watt-hours available if the battery is discharged at the standard discharge rate.
Can be calculated by multiplying the capacity (Ah) by the nominal voltage (V).
A better way to compare the “capacity” of different batteries (especially if they have different nominal voltage ratings).
Charge Ratings
Standard
Max continuous charge current
Max peak charge current
Discharge Ratings
Standard discharge current
Max continuous discharge current
Max peak discharge current
Cycle Life
References