Car battery charge and voltage: what should they be?

Important indicators of a storage battery are its capacity, voltage and electrolyte density. The quality of work and functionality of the device depends on them. In a car, the battery supplies cranking current to the starter to start the engine and supplies the vehicle electrical system when needed. Therefore, knowing the operating parameters of your battery and maintaining its performance is critical to ensure the good condition of the vehicle as a whole.

Battery voltage

To begin with, let's figure out the meaning of the term "voltage". Essentially, this is the “pressure” of charged electrons created by a current source through a circuit (wire). Electrons perform useful work (powering light bulbs, units, etc.). The voltage is measured in Volts.

You can use a multimeter to measure the battery voltage. The contact probes of the device are applied to the battery terminals. Formally, a voltage of 12V is considered the norm. The actual battery voltage should be between 12,6V -12,7V. These are the values ​​for a fully charged battery.

These figures may vary depending on environmental conditions and test time. Immediately after charging, the device can show 13V - 13,2V. Although such values ​​are also considered acceptable. To get the correct data, you need to wait an hour or two after charging.

If the voltage drops below 12 volts, then this indicates a discharge of the battery. The voltage value and charge level can be compared according to the following table.

Voltage, Volt	The degree of charge,%
12,6+	100
12,5	90
12,42	80
12,32	70
12,20	60
12,06	50
11,9	40
11,75	30
11,58	20
11,31	10
10,5	0

As you can see from the table, a voltage below 12V indicates a 50% battery discharge. The battery needs recharging urgently. You should know that in the process of discharge, the process of sulfation of the plates occurs. The density of the electrolyte drops. Sulfuric acid breaks down by participating in a chemical reaction. Lead sulfate forms on the plates. Timely charging starts this process in the opposite direction. If you allow a deep discharge, then the battery will already be difficult to reanimate. It will either completely fail, or will significantly lose in capacity.

The minimum voltage at which the battery can operate is considered to be 11,9 Volts.

Loaded and unloaded

Even at low voltage, the battery is quite capable of starting the engine. The main thing is that after that the generator will charge the battery. During the start of the engine, the battery supplies a large current to the starter, while sharply losing in charge. If the battery is healthy, the charge is gradually restored to normal values ​​within 5 seconds.

The voltage on a new battery should be in the range of 12,6 - 12,9V, but these values ​​do not always show the real state of the battery. For example, at rest, without connected consumers, the voltage is within the normal range, but under load it drops sharply and the charge is quickly consumed. This can be.

That is why measurements are taken under load. To do this, use a device such as a load plug. This test shows whether the battery is holding a charge or not.

The plug consists of a voltmeter, contact probes and a load coil in the housing. The device creates a current resistance of twice the battery capacity, simulating a starting current. For example, if the battery capacity is 50A * h, then the device loads the battery up to 100A. The main thing is to choose the right resistance. If 100A is exceeded, it will be necessary to connect two resistance coils in order to obtain accurate data.

On-load measurements are taken with a fully charged battery. The device is held for 5 seconds, then the results are recorded. Voltage drops under load. If the battery is good, it will drop to 10 volts and gradually recover to 12,4 volts and above. If the voltage drops to 9V and below, then the battery does not hold a charge and is faulty. Although after charging, it may show normal values ​​- 12,4 V or higher.

Density of electrolyte

The voltage level also indicates the density of the electrolyte. The electrolyte itself is a mixture of 35% sulfuric acid and 65% distilled water. We have already said that the concentration of sulfuric acid decreases during discharge. The larger the discharge, the lower the density. These indicators are interrelated.

To measure the density of electrolyte and other liquids, a special device is used - a hydrometer. In a normal state, with a full charge of 12,6V - 12,7V and an air temperature of 20-25 ° C, the electrolyte density should be in the range of 1,27 g / cm3 - 1,28 g / cm3.

The following table shows the dependence of the density on the charge level.

Electrolyte density, g / cm3	Charge level,%
1,27 – 1,28	100
1,25	95
1,24	90
1,23	80
1,21	70
1,20	60
1,19	50
1,17	40
1,16	30
1,14	20
1,13	10

The higher the density, the more resistant the battery is to freezing. In regions with a particularly harsh climate, where the temperature drops to -30 ° C and below, the density of the electrolyte is raised to 1,30 g / cm3 by adding sulfuric acid. The maximum density can be raised to 1,35 g / cm3. If it is higher, the acid will begin to corrode the plates and other components.

The graph below shows the hydrometer readings at different temperatures:

In winter time

In winter, many drivers find it harder to start the engine as the temperature drops. The battery stops working at full capacity. Some car enthusiasts remove the battery overnight and leave it warm. In fact, when fully charged, the voltage does not drop, but even rises.

Freezing temperatures affect the density of the electrolyte and its physical condition. When fully charged, the battery can easily endure frost, but when the density decreases, there is more water and the electrolyte can freeze. Electrochemical processes are slower.

At -10 ° C -15 ° C, a charged battery can show a charge of 12,9V. This is normal.

At -30 ° C, the battery capacity is reduced by half of the nominal. The voltage drops to 12,4V at a density of 1,28 g / cm3. Also, the battery stops charging from the generator already at -25 ° C.

As you can see, negative temperatures can significantly affect the performance of the battery.

With proper care, a liquid battery can last 5-7 years. In the warm season, the charge level and electrolyte density should be checked at least once every two to three months. In winter, at an average temperature of -10 ° C, the charge should be checked at least once every two to three weeks. In severe frosts -25 ° C-35 ° C, it is advisable to recharge the battery every five days, even with regular trips.