Yuasa Automotive Auxiliary Battery GY-AUX14 / YTX14-BS 12V 12Ah 200A (AGM backup battery)

The Yuasa GY-AUX14 (often also listed under the technical designation YTX14-BS or as an OEM spare part number) is a special AGM battery that is used in the automotive sector as an backup battery (Auxiliary Battery). It is not intended for starting the engine, but serves as a safety backup for electronic brake systems (SBC) or for stabilising the on-board network during start-stop operations. With 12 Ah and 200 A (EN), it offers exactly the specifications that vehicle manufacturers such as Mercedes-Benz require for their backup systems.

Highlights at a glance

• The Mercedes specialist: The standard replacement battery for the "small" auxiliary battery in the engine bay of many Mercedes models (e.g. E-Class W211), responsible for the SBC brake.
• AGM technology: As the battery is often installed in a hard-to-reach area, the nonwoven technology ensures absolute maintenance-free operation, leak safety and long life without topping up water.
• Safety backup: Ensures that safety-relevant systems (such as the brake or automatic transmission control) work properly even if the main battery fails or voltage fluctuations occur.
• Wet Charged (WC): This version is usually delivered factory-filled, charged and sealed, which significantly accelerates and simplifies installation in the vehicle.
• Identical dimensions: At 150 x 87 x 145 mm, it corresponds exactly to the dimensions of the original Mercedes backup battery (often Varta or Fiamm from the factory).
• High cycle stability: Designed to remain permanently in the vehicle’s trickle charge mode and to supply high currents when needed.

The life insurance for your brakes

This battery is notorious among owners of the Mercedes-Benz E-Class (W211 / S211 series), the CLS (C219) and the SL (R230). If the red message "Visit brake workshop" or a battery symbol appears in the cockpit (even though the main battery is new), it is almost always this small backup battery that is defective. It is usually located under the cabin filter in the engine bay and secures the electro-hydraulic brake (SBC).

Characteristics

FAQs for Yuasa GY-AUX14

Can I use a motorcycle battery instead?

Basically yes. The GY-AUX14 is based on the casing of the YTX14-BS motorcycle battery. The dimensions (150x87x145 mm) and performance (12Ah / 200A) are identical. Many Mercedes drivers therefore simply buy a high-quality YTX14-BS (such as this Yuasa), as it technically serves the same purpose but is often cheaper than the part with the star sticker.

Where can I find this battery in my car?

In the case of the Mercedes W211 (E-Class), this backup battery is located in the engine bay at the rear right (in the direction of travel), directly under the housing for the interior air filter (pollen filter). The filter box must be removed to access the battery. In other models, it can also be installed in the boot or under the seat.

Do I need to program the battery?

For the small backup battery (in the W211), it is generally not necessary to relearn with the diagnostic unit. After replacement, the error message in the onboard computer usually disappears by itself as soon as the system recognises the correct voltage. For start-stop batteries in newer models, programming may be required.

How do I charge this battery?

As it is an AGM battery, please use a charger with AGM mode (final charging voltage approx. 14.7 V - 14.8 V). As it only has 12 Ah, the charging current should not be too high (max. 1-2 amps recommended, e.g. with a CTEK MXS 5.0 in motorcycle mode).