Checking the battery (BMW 5 Series E39)

Checking the electrolyte level

The electrolyte level in each element should be between the MIN mark "1" and the MAX mark "2". Otherwise, unscrew the plugs "3" of the battery and top up the level with distilled water.

Checking voltage

The condition of the battery can be checked by measuring the voltage by connecting a voltmeter to its terminals.

Disconnect the battery.

Before checking, the battery must be disconnected for at least two hours.



Connect a voltmeter to the battery terminals and measure the voltage.

Conclusions based on the measurement results:

• 12.7 volts or higher - battery is in good condition;
• 12.5 volts - normal condition;
• 12.3 volts or below - the battery is in poor condition and needs to be charged or replaced.

Connect the battery.

Checking the battery under load

Connect a voltmeter to the battery terminals, start the engine and read the voltmeter reading.

During engine starting, the voltage of a fully charged battery should not fall below 10 volts (at an electrolyte temperature of approximately +20°C).

If the voltage immediately drops, and in addition, different densities of electrolyte in the battery cells were detected, then it is necessary to conclude that it is defective.

Checking the density of the electrolyte (does not apply to maintenance-free batteries)

The density of the electrolyte, along with the voltage measurement, allows you to make an accurate conclusion about the state of charge of the battery. A battery densimeter with a pipette is used for testing, which is offered at an affordable price by specialized stores. The higher the density of the electrolyte sucked by the densimeter from the battery, the more the float of the densimeter rises. The densimeter scale can be used to determine the density of the electrolyte in g / ml or in degrees Baume (+ "Be"). The state of charge of the battery corresponding to the measured density of the electrolyte is indicated below:





Check each battery element in sequence; all elements must have the same electrolyte density. The maximum permissible difference in electrolyte density in individual elements is 0.04 g/ml. Otherwise, a conclusion is made about the battery defect.

The original text is available on the website «BMWMAN»