VARTA SILVER dynamic Aux batteries

VARTA auxiliary battery: the backup for premium cars

In high-end Mercedes, BMW and Audi models the main battery does not work alone: a small auxiliary AGM battery feeds critical functions during Start-Stop, supports the electrical bus at every cranking and backs the EQ Boost / 48 V mild-hybrid system. The VARTA Silver Dynamic Aux is that second battery in compact format, with sealed AGM technology and direct OEM equivalence to original Mercedes and BMW codes.

Silver Dynamic Aux models

Signs the auxiliary battery is failing

• Dashboard warning such as "auxiliary battery malfunction" or "automatic engine stop inoperative".
• Start-Stop stops working even though the main battery is fine.
• Intermittent comfort-function glitches after cold nights.
• When replacing the main battery, check the auxiliary too: they usually age together.

Compatibility: find your exact auxiliary

Enter your plate in the battery finder by number plate or cross-check codes in the comparator to confirm the right part. Remember: OBD coding is mandatory when replacing it on these vehicles.

VARTA auxiliary battery frequently asked questions

What does a car's auxiliary battery do?

It backs up the main battery: it keeps steering, braking and electronics powered during Start-Stop and stabilises voltage at cranking. On EQ Boost mild-hybrids it also supports the 48 V system.

Which model do I need: A2, A1 or A8?

A2 (12 Ah) for Mercedes E-Class W213 and BMW 5 Series G30; A1 (13 Ah) for Mercedes S-Class W222 and BMW 7 Series G11; A8 (20 Ah) for Mercedes with EQ Boost and 48 V mild-hybrid. Verify by number plate before buying.

Can I replace the auxiliary battery myself?

Physically it is simple, but on these vehicles OBD coding is mandatory after replacement so the energy management recognises the new battery. Without coding, warnings may persist and Start-Stop may stay disabled.

What happens if the auxiliary battery is flat?

The car usually still starts on the main battery, but it disables Start-Stop and shows dashboard warnings. Replace it soon: it is the safety net for critical functions.

Catalogue curated by our technical team. 10,694 Trustpilot reviews · 4.4/5. 24h mainland delivery, free 14-day returns.