Guide To Car Battery Specifications

Batteries are complex. But if you dissect every part of the battery, you can simplify each quality and thus understand the concepts a lot better.

We will summarize the technical specifications of a car battery to help you understand how it powers your vehicle.

Nominal Voltage (V). This is the normal reference voltage of the battery.
Cut-off Voltage. This is the voltage level that refers to the “empty” battery.
Capacity or Nominal Capacity (Ah for specific C-rate). This is the Amp-hours before the battery is discharged from 100% SOC to the cut-off voltage. To compute for the capacity, the discharge current in Amps is multiplied by the discharge time and lessened as the C-rate increases.
Energy or Nominal Energy (Wh for specific C-rate). This measures the energy capacity of the battery based on the total Watt-hours from 100% SOC to the cut-off voltage. To compute for the energy, the discharge power (Watts) is multiplied by the discharge time and lessened as the C-rate increases.
Life cycle. This is the number of discharge-charge cycles that the battery has before it starts to decline. Also referred to as the cycle life, this determines the operating life of the battery as well as the humidity and the temperature. If the DOD is high, the cycle life is lessened.
Specific Energy (Wh/kg). This is the gravimetric energy density or the nominal energy of the battery per unit mass. This is usually characterized by the battery chemistry and packaging. It determines the weight of the battery to achieve the electric range required by the vehicle.
Specific Power (W/kg). This is the maximum power that is available per unit mass. It is also characterized by the battery chemistry and packaging. It determines the weight of the battery to achieve the performance target.
Energy Density (W/L). This is the volumetric energy density or the nominal energy of the battery per unit volume. It is characterized by the battery chemistry and the packaging. It determines the battery size required to reach the electric range needed by the vehicle.
Power Density (W/L). This is the maximum power that is available per unit mass. It is characterized by the battery chemistry and the packaging. It determines the battery size that will help achieve the performance target.
Maximum Continuous Discharge Current. This is the maximum current that the battery can discharge continuously without getting damaged. It is a limit set by the manufacturer. It defines the top speed and acceleration that that vehicle can sustain.
Maximum 30-sec Discharge Pulse Current. This is the maximum current that the battery can discharge at 30-sec pulses without getting damaged. It is a limit set by the manufacturer. It defines the electric vehicle’s acceleration performance.
Charge Voltage. This is the voltage level that indicates the full charge capacity. This should ideally be reached during constant voltage charging.
Float Voltage. This is the voltage level that must be maintained by the battery to compensate for its self-discharge. This should be implemented after 100% charging capacity.
Charge Current (recommended). This is the ideal current that the battery needs to be charged initially under constant charging scheme before it changes into the constant voltage charging.
Internal Resistance (maximum). This is the resistance in the battery that is separate from the charging and discharging.