Checking battery condition, care and charging (Mercedes-Benz S-Class W140)

Attention! Please also refer to the materials of the Chapter Engine electrical equipment

Attention! The intended service life of the battery is only achieved if it is always sufficiently charged. If the vehicle is used mainly for short distances or when parked for a long time, we recommend checking the charge level of the battery more often.

The battery is placed in a special niche in the right part of the luggage compartment.

Disconnecting the battery

Caution: If your car radio is equipped with an anti-theft system, make sure you enter the correct code before disconnecting the battery.

1. Do not loosen or remove the battery terminals while the engine is running. Otherwise, the electronic components may be damaged (for example, a generator).

2. Turn off all electrical consumers.

3. First disconnect and remove the negative and then the positive terminal, use a wrench. Disconnecting the wire from the battery terminal with a wrench - sometimes, in cases where corrosion has destroyed the nut, special pliers are required for this procedure (always disconnect the ground wire first and connect it last!)





4. After disconnecting the battery terminals, the electronic key in the ignition switch no longer turns, and the AT selector lever remains locked in the "P" position.

Connecting the battery

1. Make sure that all on-board electrical consumers are switched off.

2. First connect the positive terminal and then the negative terminal.

3. After connecting the battery, the following work must be carried out:

• a) Setting the clock (see Chapter User manual).
• b) Entering the radio receiver code into memory.
• c) Re-alignment of the side windows (see Chapter User manual).
• d) Re-adjustment of the sliding and lifting top hatch (see Chapter User manual).
• e) Re-align the EPS system. To do this, turn the steering wheel from lock to lock with the engine running.

Check and care

Caution: Certain safety precautions must be taken when working with the battery.

Battery cells always contain highly flammable hydrogen gas, so never allow a lit cigarette or other open flame to approach the battery.

Battery electrolyte is a sulfuric acid solution that can cause serious injury if it comes into contact with the eyes or exposed areas of the body.



In addition, acid corrodes clothing and paints. When disconnecting the battery, always disconnect the ground cable first and reconnect it last!

Prepare the necessary tools.

Tools and materials needed for battery maintenance

1. Battery maintenance is a very important procedure to avoid stopping the vehicle due to battery discharge. The maintenance procedure requires the appropriate tool.

2. Before starting any maintenance procedure, always first turn off the engine and disconnect all electrical equipment, then disconnect the battery ground cable.

Warning! If your car radio is equipped with an anti-theft system, make sure you have entered the correct code before disconnecting the battery. 3. Typically, cars of this class are equipped with batteries that do not require special care. You can remove the can lids and add distilled water. The latest models may be equipped with batteries that do not require any care at all, which are completely sealed.

4. Remove the caps and check the electrolyte level in each battery can. It should be above the plates. There is usually a level indicator on each can. If the electrolyte level is below the norm, add only distilled water and then close the can caps.

Warning! Overfilling the cans may cause electrolyte to spill over during boost charging, causing corrosion and damage to components near the battery! 5. If your vehicle's positive terminal and battery cable clamp are equipped with a rubber protector, make sure it is not torn or damaged. It must completely cover the terminal.

6. It is necessary to periodically inspect the external condition of the battery for damage such as cracks in the casing.

7. Check that the battery cable terminal clamps are tight enough to ensure a good electrical connection. Check each wire along its entire length for cracks and wear on the insulation and wires. 8. If any signs of corrosion are found, (usually presenting as a loose white coating) disconnect the wires from the terminals, clean the terminals and terminal clamps of the wires with a brush, and reconnect the latter. The occurrence of corrosion can be minimized by installing specially treated washers, which are available from auto parts stores, or by coating the terminals and terminal clamps of the wires with a layer of acid-free petroleum jelly or a suitable lubricant after they are connected.






9. Make sure that the battery tray is in good condition and that the terminal clamp bolt is securely tightened. If the battery has been removed from the tray (refer to Chapter Engine electrical equipment), describing the removal and installation procedure, make sure that no parts or other foreign objects are lying on it during installation. When tightening the terminal clamp, do not tighten its bolt too tightly.



10. Corrosion from the tray, battery case and surrounding surfaces can be removed using a solution of baking soda and water. Apply the mixture with a small brush, let it sit and then rinse with plenty of clean water.

11. Metal surfaces of the vehicle that have been subject to corrosion should be coated with a zinc-based primer and then painted.

Charger

Note: Manufacturers recommend removing the battery from the vehicle to charge it, as gas released during this procedure may damage painted surfaces or the vehicle's interior, depending on the battery's location. Rapid charging with battery cables connected may cause damage to the vehicle's electrical system.

1. Remove all caps from the battery jars (if they exist) and cover the holes with a clean rag to prevent electrolyte from spilling. Disconnect the battery ground cable and connect the charger wires to the battery terminals (positive to positive, negative to negative), then plug the charger into the mains. If it has a switch, make sure it is set to the "12V" position.

Caution: If your car radio is equipped with an anti-theft system, make sure you enter the correct code before disconnecting the battery.

2. If you are using a charger with a current greater than two amps, check the battery regularly while charging to ensure that it has not overheated. Using a slow charger, you can safely leave the battery to charge overnight after checking regularly for the first two hours. Certain precautions may be required when charging maintenance-free batteries (for example, using a very low current charger). There may be a warning label on such a battery, but if there is none, consult the manufacturer's representative office or an electrician at a car repair shop.



3. If the battery jars have removable caps, check the specific gravity of the electrolyte with a hydrometer every hour during the last few hours of the charge cycle. Inexpensive hydrometers are available at auto parts stores - follow the instructions on the package when using them. The battery is considered charged if the specific gravity of the electrolyte does not change over two hours and the electrolyte in the jars bubbles freely. The specific gravity of the electrolyte in the individual jars should be nearly the same. If this is not the case, one or more of the battery jars is bad and should be replaced.

4. Some maintenance-free batteries have a built-in hydrometer at the top, which has a window - a color indicator of the battery charge level. Usually, a brightly colored window means that the battery is fully charged, and a dark color indicates that additional charging is needed. More precise information is provided in the battery manufacturer's instructions.

5. If the battery is sealed and does not have a built-in hydrometer, you can check the charge level by connecting a digital voltmeter to the battery terminals. A fully charged battery will show 12.6 volts or more.

6. Additional information about the battery and jump starting can be found in Introduction to this Manual.