Totally Discharged Batteries, Charging

WARNING: This page does not describe the selected car, but rather 16 other vehicles, including the 2009 Audi S4, 2009 Audi A4, 2008 Audi S4, 2008 Audi RS 4, and 2008 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

Batteries which have not been used for lengthy periods, e.g. in vehicles which have not been driven, are subject to self-discharge.

Batteries are considered to be severely discharged if open-circuit voltage drops below 11.6 V. With voltage between 12.2 and 11.6 V, the battery is pre-damaged. Measure no-load voltage:

Vehicles without Energy Management Control Module J644 → Battery No-Load Voltage - Vehicles without Energy Management Control Module, Checking .

Vehicles with Energy Management Control Module J644 → Battery No-Load Voltage - Vehicles with Energy Management Control Module, Checking .

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

Severely discharged batteries become sulfated, i.e. 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 a severely 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.

CAUTION: Risk of injury from battery acid.

Prior to handling or servicing batteries, read, understand and observe the Warnings and Safety Measures for lead-acid batteries for lead-acid batteries → Safety Precautions !
Wear protective eyewear and clothing → 27 - Battery, Starter, Generator, Cruise control .
On non-maintenance-free batteries, the sealing plugs must be installed tightly.
Provide sufficient ventilation.

If the magic eye 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.
DO NOT battery test batteries which are gassing. Otherwise there is a risk of explosion.
Rapid-charging batteries → Battery, Quick Charging .
Dispose of electrolyte (sulfuric acid/water mixture) properly! Waste electrolyte must only be disposed of in appropriate waste disposal sites. Refer to local regulations pertaining to electrolyte disposal.

The following notes and procedures must be followed to ensure correct charging.

CAUTION: Risk of severely discharged batteries freezing.

Severely discharged batteries freeze at low temperatures, the housing can crack.
Batteries that have frozen must no longer be used.

Prerequisite

Battery temperature must be at least +10 C.

Procedure

Severely discharged (sulfated) batteries must be charged using a low charging current:

NOTE:

The Midtronics Diagnostic Conductance Charging Station INC-940 automatically detects severely discharged batteries and carefully starts the charging procedure with a low charging current. The charge current is automatically adjusted to the battery charge state.
In order to initiate charging procedure, battery voltage must be at least 0.6 V!

CAUTION: Risk of damaging severely discharged batteries.

Do not quick charge severely discharged batteries.

Charge battery → Battery, Charging with Midtronics Diagnostic Conductance Charging Station INC-940 .

The charging voltage may be a maximum of 14.4 V.

NOTE:

If battery is replaced, follow disposal regulations → 27 - Battery, Starter, Generator, Cruise control .