Car Battery – Automotive Battery
A car or automotive battery is a rechargeable battery used to start a motor vehicle. It is also known as the SLI battery. The term SLI refers to starting, lighting, and ignition. Its main purpose is to provide an electric current to the electric-powered starting motor, which in turn starts the chemically-powered internal combustion engine that actually propels the vehicle. Once the engine is running, power for the car’s electrical systems is still supplied by the battery, with the alternator charging the battery as demands increase or decrease.
Car batteries are designed to deliver the maximum current in a short space of time, keeping the voltage constant, therefore, they have a very low internal resistance. These batteries have a good life under shallow-cycle conditions but have a very poor lifetime under deep cycling (around 12-15 cycles). Current discharges might be with strong temperature changes, which is why the weight, design, and shape are characteristic. These types of batteries are usually frequent for starting cars and all types of diesel and gasoline vehicles.
Characteristics of Car Batteries
To compare and understand the capability of each battery, some important parameters are characteristic of each battery, also within a type of battery. These parameters are a reference when a battery is needed, and specific qualities are required since batteries are used in all types of devices and for infinite purposes.
Cell Voltage
The voltage of electric batteries is created by the potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction.
A common voltage for automobile batteries is 12 volts (DC). But this battery consists of six 2V lead cells.
Cut-off Voltage
The cut-off voltage is the minimum allowable voltage. It is this voltage that generally defines the “empty” state of the battery.
The truth is that any lead acid battery, be it a Gel Cell, AGM or flooded batteries, should be cut off at 11.6 volts.
Capacity
The coulometric capacity is the total Amp-hours available when the battery is discharged at a certain discharge current from 100% SOC to the cut-off voltage.
A common voltage for automobile batteries is 12 volts (DC). But this battery consists of six 2V lead cells. An average automotive battery might have a capacity of about 70 Ah, specified at a current of 3.5 A.
C-rate of Battery
C-rate is used to express how fast a battery is discharged or charged relative to its maximum capacity. It has units h−1. A 1C rate means that the discharge current will discharge the entire battery in 1 hour.
Self-discharge
Batteries gradually self-discharge even if not connected and delivering current. This is due to non-current-producing “side” chemical reactions that occur within the cell even when no load is applied.
A lead acid battery left in storage at moderate temperatures has an estimated self-discharge rate of 5% per month. This rate increases as temperatures rise and the risk of sulfation increases.
Degradation
Some degradation of rechargeable batteries occurs on each charge–discharge cycle. Degradation usually occurs because electrolyte migrates away from the electrodes or because active material detaches from the electrodes.
Deep cycle batteries can provide 200 to more than 3000 discharge/charge cycles. Starting batteries are not designed for sustained discharge and will last for only 50-60 use cycles.
Depth of Discharge
Depth of discharge is a measure of how much energy has been withdrawn from a battery and is expressed as a percentage of full capacity. For example, a 100 Ah battery from which 40 Ah has been withdrawn has undergone a 40% depth of discharge (DOD).
