Most retailers offer a simple free five minute battery test. With experience, one can accurately determine state of charge using a voltmeter. Battery voltage reacts highly to charging and discharging. When a car drops, for instance, from 12.6 to 12.0, there will be 75% difference.
Measuring your car battery’s voltage can be a great way to determine how charged your battery might be. The charge time is 12–16 hours and up to 36–48 hours for large stationary batteries.
A fully charged car battery voltage should be 12.6v or above, this is with the engine off.
A regulated current raises the terminal voltage until the upper charge voltage limit is reached, at which point the current drops due to saturation. [2] X Research source Battery voltage state of charge table. Percentage of Charge 12 Volt Battery Voltage Specific Gravity 100 12.70 1.265
That is, when the deep cycle battery isn’t under load and hasn’t been under load for a few hours. To get a true voltage reading of the cars battery it is important to measure the voltage after the car has been sat for a period with the engine off, preferably overnight, this provides you with the “car battery open circuit voltage” or also know as the “resting voltage”.
Connect your voltmeter's positive lead to the positive terminal on your battery.
Proactively testing it (or making sure your mechanic does) twice a year will help reduce your chances of failure. Voltages and Specific Gravity are listed for a 6-volt or 12-volt battery, and battery banks of 24 and 48 volts. The lead acid battery uses the constant current constant voltage (CCCV) charge method. Fully charged voltage. The ideal car battery voltage range will provide you with a relevant interval according to which you can measure precisely what the voltage says about the battery’s current charge. Car battery chargers run off AC power and provide 12V DC at relatively low voltages, which is the best way to charge a completely dead battery. I put together the following battery state of charge chart which indicates the state-of-charge (percent) as it relates to battery voltage or specific gravity.
Check Battery Voltage and State of Charge Battery Storage; Car Battery Testing & Voltage. As a battery is charged the indicated voltage increases and, as discharging occurs, the indicated voltage decreases.
Note: The figures are based on open circuit readings. The chart is listed below.
But first, a few important notes and caveats… The positive lead on a voltmeter is usually red. At 12.4 volts, a car battery is 75% charged while at 12.2 volts its 50% charged. It’s important to test your battery and electrical system regularly, not just when it’s starting to show signs of weakness. Its power drops from 100% to 25%.
Consider your car battery charged at 12.4 volts or higher and discharged at 12.39 volts or less. Charging a dead battery with an excessively high voltage can increase the off-gassing of hydrogen, which can, in turn, result in a hazardous situation where the battery …
The table below shows the voltage and approximate state of charge for each type of battery.