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Exhaustively Discharged Battery







Exhaustively Discharged Battery

Batteries that have not been used in driving operation for a long time, for example in stored vehicles, discharge themselves.

Batteries are considered to be exhaustively discharged if the no load voltage drops below 11.6 volts. In the case of extended downtime under 12.2 volts, the battery is prematurely damaged.

Measure the no load voltage in vehicles without a battery monitoring control module (J367) or energy management control module (J644). Refer to => [ Measuring the No Load Voltage ] Measuring the No Load Voltage.

In vehicles with a battery monitoring control module or energy management control module, perform a battery test with the diagnostic systems (VAS 5051B), (VAS 5052), and (VAS 5053). Refer to => [ Battery Check using Diagnostic Systems VAS 5051B, VAS 5052 and VAS 5053 ] Battery Checking, Vehicles with a Battery Monitoring Control Module or Energy Management Control Module.

With exhaustively discharged batteries, the battery acid (mixture of sulfuric acid and water) is mostly water, with a greatly reduced sulfuric acid content.

Exhaustively discharged batteries become sulfated, for example, all the plate surfaces of such batteries become hardened. Instead of being transparent, the electrolyte has a slightly milky appearance.

The sulfating process may be reversed if an exhaustively discharged battery is recharged immediately.

If battery is not recharged, plates will continue to harden, and ability to accept a charge will diminish. This results in reduction of battery performance.

Procedure

The battery temperature must be at least 10 °C (50 °F).


Risk of explosion on discharged battery with "visual indicator".

If the "visual indicator" has no color or is light yellow, the battery may not be tested or charged. Jump starting must not be used! There is a risk of explosion during testing, charging or jump starting. The battery must be replaced.


Risk of exhaustively discharged batteries freezing.

Exhaustively discharged batteries freeze at low temperatures, the housing can crack.

Batteries that have frozen must no longer be used.

Discharged sulfated batteries must be charged as follows using a low charging current:

- Adjust the charge current to approximately 5% of the battery capacity, for example, the charging current for a 60 Ah battery is then approximately 3 ampere.

The battery voltage must be at least 0.6 volt!

The (VAS 5095A), (VAS 5900), (VAS 5903), (VAS 5904) and (VAS 5906) battery chargers automatically detect exhaustively discharged batteries and carefully start the charging procedure with a low charging current. The charge current is automatically adjusted to the battery charge state.


Risk of damaging exhaustively discharged batteries.

Do not rapid charge exhaustively discharged batteries.

- Charge the battery. Refer to => [ Battery Charger, Charging the Battery ] Battery Charger, Charging the Battery.

The charging voltage may be a maximum of 14.4 volts.

If the battery must be replaced, follow the disposal regulations. Refer to => [ Pollution risk. ] Lead Acid Battery Warnings and Safety Precautions.