Your Audi A8 is equipped with two 12 Volt batteries and a high-voltage battery.
When the 12 Volt batteries are discharged, you can, as with a conventional Audi A8, charge them using a battery charger or start the Audi A8 using jump leads connected to the battery of another Audi A8.
This also applies if the high-voltage battery is discharged. However, the charging process is described via driver messages in the instrument cluster display. To this end, the ignition must be switched on and all electrical systems that are not required must be switched off.
The battery is charged/the Audi A8 is jump-started using the connections in the engine compartment Link/Link.
Audi A8 is not ready to start. See owner's manual
This driver message appears if the charge of the high-voltage battery is too low. The Audi A8 can no longer be started under its own power. The high-voltage battery must be charged using a battery charger or the Audi A8 started using jump leads connected to the battery of another Audi A8.
After connecting the battery charger or jump-lead, the ignition must remain off for about two minutes before being switched on again. A maximum of one minute later, one of the following indicator/warning lamps will light up in the instrument cluster.
Charging battery. Please wait...When the indicator lamp and the driver message appear, the high-voltage battery is being charged or the Audi A8 is being started using jump leads connected to the battery of another Audi A8.
If the 12 Volt batteries are also discharged, the warning lamp 
lights up. The charging process takes longer in this case as the 12 Volt batteries have to be charged first. The process takes less time if the ignition is switched off.
lights up. The charging process takes longer in this case as the 12 Volt batteries have to be charged first. The process takes less time if the ignition is switched off.Audi A8 ready to start.
This message appears if the charging process was successful. The Audi A8 can once again be started.
Battery could not be charged sufficiently to start Audi A8
This message appears if the charging process was not successful or if it was interrupted. This could have been caused by a weak battery charger or a weak battery in the Audi A8 providing the electric power. If the Audi A8 cannot be started, please obtain professional assistance.
Note
- The battery charger should have an amp rating of at least 30 A; otherwise it will take significantly longer to charge the high-voltage battery. An amp rating of 50 A to 70 A is ideal.
- The Audi A8 being used to jump-start your Audi A8 should be approximately in the same Audi A8 class. A smaller Audi A8 could have its battery completely discharged.
- After about 30 minutes, the charging process will be interrupted as the ignition is switched off automatically. Switch the ignition back on if you wish to continue the charging process.