Checking and refilling levels
228charge. Never short the battery terminals. High-energy sparks can cause 
injury.•
A highly explosive mixture of gases is released when the battery is 
under charge. The batteries should be  charged in a well-ventilated room 
only.
•
Keep children away from acid and batteries.
•
Before working on the electrical system, you must switch off the 
engine, the ignition and all consumers. The negative cable on the battery 
must be disconnected. When a light bulb is changed, you need only switch 
off the light.
•
Deactivate the anti-theft alarm by unlocking the vehicle before you 
disconnect the battery! The alarm will otherwise be triggered.
•
When disconnecting the battery from the vehicle electrical system, 
disconnect first the negative cable and then the positive cable.
•
Switch off all electrical consumers before reconnecting the battery. 
Reconnect first the positive cable and  then the negative cable. Never 
reverse the polarity of the connections. This could cause an electrical fire.
•
Never charge a frozen battery, or one which has thawed. This could 
result in explosions and chemical burns. Always replace a battery which 
has frozen. A flat battery can freeze at temperatures around 0°
•
Ensure that the vent hose is always connected to the battery.
•
Never use a defective battery. This may be fatally explosive. Replace a 
damaged battery immediately.Caution
•
Never disconnect the  battery if the ignition is switched on or if the engine 
is running. This could damage the electrical system or electronic compo-
nents.
•
Do not expose the battery to direct sunlight over a long period of time, as 
the intense ultraviolet radiation can damage the battery housing.
•
If the vehicle is left standing in cold conditions for a long period, protect 
the battery from frost. If it “freezes” it will be damaged.
Checking the electrolyte level
The electrolyte level should be checked regularly in high-
mileage vehicles, in hot countries and in older batteries.– Open the bonnet and open the battery cover at the front  ⇒ in 
“Safety instructions on working in the engine compartment” on 
page 213  ⇒ in “Warnings on handling the battery” on 
page 227.
– Check the colour display in the "magic eye" on the top of the  battery.
– If there are air bubbles in the window, tap the window gently until  they disperse.The position of the battery is show n in the corresponding engine compart-
ment diagram  ⇒page 273.
The round window (“magic eye”) on the top of the battery changes colour, 
depending on the charge level and electrolyte level of the battery.
If the colour in the window is  colourless or bright yellow, the electrolyte level 
of the battery is too low. Have the battery checked by a qualified workshop.
The colours green and black are used by the workshops for diagnostic 
purposes.
WARNING (continued)
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