Air bubbles can influence the colour of the indicator. For this reason carefully
knock on the indicator before carrying out the check.
Checking
Black colour - electrolyte level is correct.
Colourless or light yellow colour - electrolyte level too low, the battery must be
replaced.
For technical reasons, the electrolyte level cannot be checked on vehicles with
the designation “AGM” .
Vehicles with the START STOPsystem are fitted with a battery control unit for
checking the energy level for recurring engine starts.
We recommend that you have the acid level checked regularly by a specialist
garage, especially in the following cases. ▶ High external temperatures.
▶ Longer day trips.
▶ After each charge.
Winter time
The vehicle battery only has a proportion of the starting power in lower tem-
peratures. A discharged vehicle battery may already freeze at temperatures
just below 0 °C .
We therefore recommend that you have the battery checked and, if necessary,
recharged by a specialist garage before the start of the winter.
Note
The battery acid level is also checked regularly by a specialist garage as part of
the inspection service.
Charging
Read and observe
and on page 172 first.
A properly charged vehicle battery is essential for reliably starting the engine.
A charging operation can be performed if the following conditions are satis-
fied.
The engine is turned off.
The ignition is switched off.
All consumers are turned off.
The bonnet is open.
“Fast charging” with high currents›Disconnect both battery cables (first of all “negative”, then “positive”).›
Attach the terminal clamps of the charger to the battery terminals (red =
“positive”, black = “negative”).
›
Plug the mains cable of the charger into the power socket and switch on the
device.
›
After charging has been successful: Switch off the charger and remove the
mains cable from the power socket.
›
Only then disconnect the charger's terminal clamps.
›
Reconnect the cables to the battery (first “positive”, then “negative”).
Charging with low voltages
It is not necessary to disconnect the cables from the battery if you recharge
the vehicle battery, for example from a mini-charger.
Refer to the instructions of the charger manufacturer .
A charging current of 0.1 multiple of the total vehicle battery capacity (or low-
er) must be used until full charging is achieved.
The vent plugs of the vehicle battery should not be opened for charging.
WARNING■ When you charge a battery, hydrogen is released, and a highly explosive
gas mixture is also produced. An explosion can be caused through sparkling
over during unclamping or loosening of the cable plug while the ignition is
on.■
Creating a bridge between the poles on the battery (e.g. with metal ob-
jects - cables) creates a short circuit - risk of damage to the battery, explo-
sion and burning of the battery, jets of acid spurting out.
■
Avoid creating sparks when working with cables and electrical devices.
Strong sparking represents a risk of injury.
■
Before carrying out any work on the electrical system, switch off the en-
gine, the ignition and all electrical consumers and disconnect the negative
terminal
.
■
“Quick-charging” the vehicle battery is dangerous and requires a special
charger and specialist knowledge.
■
We therefore recommend that vehicle batteries be “rapidly charged” by a
specialist garage.
174General Maintenance
