12 volts is the standard automotive battery in today’s vehicle and each of the battery has 6 cells with a voltage of 2.1. A fully charged car battery has 12.6 volts.
There is a very big difference when a car battery drops even a small amount of voltage. When a car drops, for instance, from 12.6 to 12.0, there will be 75% difference. Its power drops from 100% to 25%. At 12.4 volts, a car battery is 75% charged while at 12.2 volts its 50% charged.
Consider your car battery charged at 12.4 volts or higher and discharged at 12.39 volts or less.
Check Battery Voltage and State of Charge
It is important that you first check the battery plus the charging system output (alternator). Turn on the headlights if they come on with normal brightness it’s possible the no crank problem is not the battery. The problem could be one of the following:
- bad starter relay or solenoid
- a poor wiring connection between the relay and starter or
- Dim or no headlights at all, check on the battery voltage and charging output.
You will need a voltmeter for this. First you select 12 or 20 voltmeter scale then connect the voltmeter red positive test lead to the battery positive terminal (+) and also the black negative test lead to the battery negative terminal (-).
In case the battery has a reading of 12.4 from the voltmeter, it means it is low (discharged) and should be recharged. A battery fully charged has a reading of about 12.6 volts.
Check Car Battery Charging Voltage
You should connect the voltmeter to the battery as before but not the charging voltage and this should be done after charging the battery or jump starting the car. 13.5 to 14.5 or more volts at idle should be produced by a charging system that operates normally. The alternator may not be putting out enough current to keep the battery charged if the charging voltage is less than 13.5 volts. Make sure the alternator is tested (can be tested at an auto parts store). Consider replacing the alternator if the current output is not up to specifications.
After recharging the battery, test it to find out if it is capable of holding a charge. Do this by use of a hand held electronic battery tester or a conventional load tester. If the battery is good or bad, be sure that the tester will tell you. It is important to note that for accurate test results load testers require the battery to be fully charged. Reliable test results are given by most electronic testers even if the battery is not fully charged. Replace a battery if it fails a load test.
12V Car Battery Voltage Chart
The average duration a car battery can last is 4 to 5 years or even 3 years in hot climates such as Arizona and Florida. Therefore if your battery is more than 4 years old and car battery voltage drops quickly, it is possible it has reached the peak of its useful service life and requires replacement especially if it does not hold a charge but it has a normal working charging system.