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.