# TUDOR AUXILIARY Batteries

> Tudor Auxiliary AGM battery for Mercedes, BMW and Audi twin-battery cars: TX12, TX13 and TX20, 12-20 Ah. OBD coding required, 24h mainland delivery.

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## Description

**Tudor Auxiliary batteries** are AGM back-up batteries for premium cars with a twin-battery layout: a main 12V battery cranks the engine, while the auxiliary unit supports Start-Stop and the on-board electronics whenever the engine is off. Tudor is the European-built brand of the Exide Group, and this range covers 12 to 20 Ah.
It is the usual **auxiliary battery** for Mercedes, BMW and Audi models fitted with a second battery, including 48V mild-hybrids. A direct counterpart to the [VARTA Silver Dynamic Aux](/gb/batteries-varta-silver-dynamic-aux), it requires OBD coding after replacement.

## Tudor auxiliary AGM battery: reliable back-up for your second battery

Many recent Mercedes, BMW and Audi models run two batteries: the main one handles engine starting, while the **auxiliary battery** keeps Start-Stop, the electric parking brake and other systems powered when the engine is off. The **Tudor Auxiliary** range does that job with **sealed, maintenance-free AGM** technology, safe to mount inside the cabin or boot with no risk of leaks.
When the auxiliary battery wears out, the dashboard usually shows an auxiliary battery malfunction warning and Start-Stop stops working, even though the car still starts normally.

### Models in the Tudor Auxiliary range

- **Tudor TX12** (12 Ah): auxiliary battery for Mercedes E-Class W213 and BMW 5 Series.
- **Tudor TX13** (13 Ah): designed for Mercedes S-Class and BMW 7 Series.
- **Tudor TX20** (20 Ah): back-up battery for 48V mild-hybrid systems.

### Compatibility: choosing the right auxiliary battery

Find the exact model your car uses in our [battery comparator](/gb/comparator) or look it up with the [battery finder by number plate](/gb/battery-finder-by-plate). After fitting, **OBD coding is mandatory** so the charging management recognises the new battery.

## Frequently asked questions about the Tudor Auxiliary battery

### **What is the difference between the main and the auxiliary battery?**

The main battery cranks the engine; the Tudor Auxiliary, at 12 to 20 Ah, backs up Start-Stop and the electronics while the engine is off. They are different batteries and not interchangeable.

### **Does the auxiliary battery need OBD coding?**

Yes. On Mercedes, BMW and Audi, OBD coding is mandatory after replacement so the energy management system applies the correct charging curve to the new battery.

### **Is it equivalent to the VARTA Silver Dynamic Aux?**

Yes. The Tudor Auxiliary range is the direct counterpart of the VARTA Silver Dynamic Aux: same AGM technology and same applications, built in Europe by the Exide Group.

### **How long does an auxiliary AGM battery last?**

Under normal use, an auxiliary AGM battery typically lasts 4 to 6 years. It needs no maintenance, but replace it as soon as the dashboard warns you, to avoid overworking the main battery.

Catalogue curated by our technical team. **11,009 Trustpilot reviews · 4.5/5**. 24h mainland delivery, free 14-day returns.

## Products in this category

| Product | Brand | Price |
|---|---|---|
| [Car battery Tudor TK143 12V 14Ah 80A AGM](https://baterias.com/gb/battery-tudor-tk143-12v-14ah-80a) | TUDOR | 52,48 € |
| [Car battery Tudor TK151 12V 15Ah 200A AGM](https://baterias.com/gb/battery-tudor-tk151-15ah-200a) | TUDOR | 64,30 € |
| [Car battery Tudor TK111 12V 11Ah 150A AGM](https://baterias.com/gb/battery-tudor-tk111-11ah-150a) | TUDOR | 169,00 € |
| [Car battery Tudor TK091 12V 9Ah 120A AGM](https://baterias.com/gb/battery-tudor-tk091-9ah-120a) | TUDOR | 61,07 € |

## Technical team (editorial authorship)

The FAQs, guides and comparisons on this site are reviewed by the baterias.com technical team — over 25 years of experience validating automotive batteries.

→ https://baterias.com/gb/technical-team

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*baterias.com — Automotive batteries · 2026-08-06*