flynavy

If I disconnect the battery ground, what will I experience when it is reconnected? Should I buy a 9v cigarette lighter memory minder or is that a gimmick? I would assume that the systems should just work but before I do anything I want to be sure.
Thanks in advance!

smith2010Q7

a 9v battery works on old technology cars. Most cars including the Q7 has too many electrical systems require a 12V system it keep it alive.

Audi has the tool VAS 5903 hook up when working on the cars.

Charging battery in support mode with battery charger -VAS 5903-
General notes:
The support mode provides the onboard supply with power when the battery is removed or disconnected.
For further information, refer to the → operating manual VAS 5903.
The support mode is suitable in the following situations:
- Support mode of onboard supplies without installed battery
- Power conservation when renewing the battery
- Ancillaries test without battery
WARNING
Danger of injury! Observe warning notices and safety regulations → Chapter!
WARNING
It is not permissible to test or charge batteries whose magic eye shows light yellow. Do not slave/jump start the vehicle!
Danger of explosion when checking and charging or slave/jump starting.
These batteries must be renewed.
– Switch off ignition and all electrical consumers.
Caution
The terminal polarity protection in operating mode „charging totally discharged batteries/support mode“ is not active. Connect battery charger terminal clamps correctly to battery terminals.
It can cause sparks through a short-circuit.
Danger of explosion
Ensure charger terminal clamps are seated securely.
Do not press START / STOP button when charger unit cables are connected incorrectly. The charger unit may be damaged.
– Remove battery.
– Connect charger plug to battery charger. The last selected operating mode will appear on display → Chapter.
Caution
When battery is removed, ensure there is no contact between terminal clamp connected to positive clamp and body earth. Also ensure there is no contact between battery clamps.
– Connect red terminal clamp „+“ to positive terminal of vehicle.
Note
In vehicles with start/stop function and battery monitor control unit -J367- fitted, black terminal clamp must be connected to body earth. Connecting it to battery negative terminal will cause start/stop system to malfunction.
– Connect black terminal clamp „+“ to negative terminal of vehicle.
– Press START / STOP for approx. 5 seconds. The menu „charging totally discharged batteries/support mode“ will be activated.
– Press respective button „Up“↑ or „Down“↓ to set respective battery voltage (6 V, 12 V or 24 V).
Note
If a button is not pressed within 5 seconds the charger will return to the main menu (select operating mode).
– Confirm the selected battery voltage with START / STOP.
Then follows the enquiry for "is charger cable terminal polarity correct".
– Check polarity of charger unit cables.
– Confirm polarity of charger unit cables with START / STOP.
The battery charger starts with support mode.
End battery support mode:
– Press START / STOP.
– Disconnect black terminal clamp „-“ of charger unit from negative terminal of vehicle.
– Disconnect red terminal clamp „+“ of charger unit from positive terminal of vehicle.
– Pull charger plug out of battery charger.
General Information Awards Operating System Disconnects
Display Cases Support Repair Manual