9Ah auxiliary battery
The 9Ah auxiliary battery is used to provide power to neccesary electrical consumers when the engine is being started, to avoid power interruptions.
Original battery made by Hoppecke
If your radio and instrument cluster loses power when the engine is restarting - the first thing to do is replace this battery!!!
Genuine volkswagen part number: 1H0 915 105 E (1H0915105E) OEM replacement (Varta): Varta Funstart YB9L-A2 (509 016 008) - 12V 9Ah 80A (EN) - I use this myself.
Width: 75mm Length: 135mm Height: 139mm