Built-in battery indicator
The indicator is green - The battery has a sufficient degree of charge.
The indicator is black - The battery needs to be charged.
The battery of the BMW 3 Series has an integrated battery charge indicator (arrow illustration), located on the top side of the battery. This "magic eye" can, of course, show only the ground state of charge.
The battery does not require maintenance. The addition of distilled water is not required. The electrolyte level can be determined from the outside. It is located at the MAX -1- mark, approximately 5 mm above the lead plates.
Checking the electrolyte level (batteries requiring maintenance)
If a non-BMW battery is purchased, it is usually a so-called low-maintenance battery. In this case, if the electrolyte level drops below the MIN·mark, it is necessary to add distilled water once or twice a year. All battery sections must have the same electrolyte level between the MAX and MIN·marks.
The electrolyte level must be checked externally. If this is not possible, remove the screw caps and look into the section from above. The electrolyte level should be 5 mm above the lead plates.
Electrolyte Density Check
The density of the electrolyte, combined with the voltage of the battery, gives an indication of the state of charge of the battery.
The temperature of the electrolyte during measurement should not be lower than +10°C.
1. Turn off the ignition.
2. Turn out stoppers from all sections of the battery. If there is a cover strip, first remove it with a screwdriver.
3. Immerse the densimeter in the electrolyte and suck out enough electrolyte to make the float float. The higher the specific gravity (density) electrolyte sample taken, the more the float pops up. On the scale of the device, you can read the value of the specific gravity (g/ml) or degrees Baumé (+°Be).
4. The density of the electrolyte must be at least 1.20 g/ml. If the density value is lower, the battery needs to be charged. Please refer to Specifications.
5. Check each section of the battery one by one. All sections must have the same density (maximum difference 0.04 g/ml). A large difference indicates battery damage.
Checking the resting voltage of the battery
The condition of the battery is checked by measuring the voltage between the poles of the battery with a voltmeter.
6. Disconnect the battery poles, refer to Section Removing and installing the battery.
7. The battery must be disconnected 2 hours before testing.
8. Attach a voltmeter to the battery terminals and measure the voltage.
9. Evaluation of measurement results:
12.5V or higher - battery is in good condition
12.4 V or below - the battery is in poor condition, needs to be charged or replaced
10. Connect the negative cable (-) battery, refer to Section Removing and installing the battery.
Checking battery voltage under load
11. Attach a voltmeter to the battery poles.
12. Ask an assistant to start the engine and read the voltage.
13. In the process of starting when the battery is fully charged, the voltage should not fall below 10 V (at an electrolyte temperature of about +20°С).
14. If the voltage immediately drops and the density of the electrolyte in the sections is different, then the battery is damaged.