Car Battery Voltage


Electric energy for running an automobile is supplied by the automotive battery. Based on its uses, Starting, Lighting, and ignition, these batteries are known as SLI batteries.  The batteries are all rechargeable type. SLI batteries are normally lead acid type. They are made of 6 galvanic cells connected in series to provide a Car Battery Voltage of 12 Volt system. (Each cell provides 2.1 Volts for the total of 12.6 Volts). Some of heavy duty vehicles such as large tucks may have a battery system voltage of 24 Volts.

System function

Lead-acid batteries consist of plate of lead and separate plates of lead dioxide. These plates are submerged into an electrolyte solution of 38% sulfuric acid and 62% water. A chemical reaction starts releasing electrons allowing them to flow through the conductors to produce electricity. Even as the battery discharges, the acid in the electrolyte reacts with the materials of the plates changing their surface to lead sulfate. When the battery is recharged, the chemical reaction is reversed. In this revere reaction, the lead sulfate reforms into lead oxide and lead as per the original condition. This process operates as a cycle as the battery is in use.

Car Battery Voltage

As the automotive batteries go through the process of charging, use and recharging, there is no need for any resources required for manufacture of new batteries. This facility also diverts toxic lead from landfills and also prevents the risk of improper disposal.

Battery recycling of automotive batteries reduces the need for resources required for manufacture of new batteries, diverts toxic lead from landfills, and prevents risk of improper disposal.

Car battery voltage & its importance

The voltage on the standard automotive battery in today’s vehicle is 12.6 Volts. Each of the battery has 6 cells with a voltage of 2.1. A fully charged car battery has 12.6 volts.

This voltage level is very essential as even if the voltage drops to 12 Volts from 12.6 Volts, there will be a 75% difference. It is very essential to check the battery and the charging system output (alternator). The open circuit voltage, is measured when the engine is off and no loads are connected. It can be approximately related to the charge of the battery. The power of the battery drops from 100% to 25%. Further, at a voltage level of 12.4 Volts, an automotive battery is 75% charged. At 12.2 Volts level, it is only 50% charged.

Voltage details

The following is common for a six-cell automotive lead-acid battery at room temperature:

a)    After full charge the terminal voltage will increase quickly to 13.2 V and then drop slowly to 12.6 V
b)    Charge with 13.2–14.4 V
c)    Continuous-preservation charge with max. 13.2 V
d)    Fully discharged: 11.8 V
e)    Gassing voltage: 14.4 V
f)    Open circuit voltage is measured 12 hours after charging to allow surface charge to dissipate and enable a more accurate reading.
g)    Quiescent (open-circuit) voltage at full charge: 12.6 V

All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature changes (negative temperature coefficient – lower voltage at higher temperature).

Testing the recharged condition of the battery

After recharging, the battery has to be tested to confirm whether it is capable of holding a charge. A conventional load tester or a hand-held battery tester may be used for this purpose. The tester will confirm whether the battery is good or bad. It is important to note that the battery should be fully recharged for accurate results. If the battery fails the load test, it needs to be replaced.

Life of automotive SLI battery

The average performing period for an automotive battery is 4 to 5 years (in hot climates, this may even be reduced to 3 years). If the battery is more than 4 years old, it is advisable to note that it has reached the peak of its useful service and needs to be replaced.

Types and brands available & tips

a)    Solar powered car battery charger ? tips – park the car outside the house for best effects.
b)    Varta Battery
c)    Optima Battery
d)    Odyssey battery
e)    AC Delco batteries
f)    AutoCraft Battery
g)    Bosch car batteries


Car Battery Voltage level is an important factor for the good upkeep and performance of the vehicle.