What's the difference between the main and the auxiliary battery?

The main battery starts the engine and handles general loads; the auxiliary is a second, smaller 12V battery backing up critical systems when the engine is off or in electric mode.

Can I fit any 12V auxiliary battery in my car?

No. It must match the original in capacity (Ah), dimensions and technology (usually AGM), since the vehicle's energy-management system is calibrated for that exact reference.

How long does an auxiliary battery last?

Working in short, frequent cycles, it typically lasts 4-6 years, similar to a well-maintained AGM starter battery.

What happens if the auxiliary battery fails?

The car may show electrical fault warnings, disable advanced Start-Stop or lose comfort features with the engine off, even if the main battery is healthy.

How do I find the exact capacity of my original auxiliary battery?

Check the label on the fitted battery, or enter your vehicle in our finder — we'll show the compatible AGM reference by Ah, dimensions and polarity.

12,161 customer reviewsThank you for trusting usThank you! Excellent 4.5 out of 5

Auxiliary Batteries

Auxiliary batteries (12V, or 5V lithium-ion on some hybrids) power the secondary electrical systems of modern cars such as BMW 5 Series/7 Series, Mercedes E/S-Class/AMG, Audi A6/A7/A8, VW Touareg and Porsche Panamera/Cayenne. They are compact (5-15 Ah) and almost always AGM, the sealed technology that copes best with tight spaces and any mounting position.

This backup or auxiliary car battery keeps critical systems running — onboard computer, alarm, central locking — when the engine is off and the main battery is disconnected, typical of advanced Start-Stop or mild-hybrid electric mode. Without it, the car may throw electrical fault warnings or lose comfort features whenever the engine stops.

Subcategories

FULBAT Auxiliary AGM

There are 38 products.

Sort by:

VARTA

Car battery Varta AUX14 12V 13Ah 200A

12V

13Ah

200A

AGM

150 × 87 × 146 mm

5,00(1)

€70.20 VAT incl.

Cookie	Provider	Purpose	Expiry
PHP_SESSID	baterias.com	The PHPSESSID cookie is native to PHP and allows websites to store serialised status data. On the website it is used to establish a user session and to pass state data through a temporary cookie, which is commonly known as a session cookie. These Cookies will only remain on your computer until you close your browser.	Session
PrestaShop-#	baterias.com	This is a cookie used by Prestashop to store information and keep the user's session open. It stores information such as currency, language, customer ID, among other data necessary for the proper functioning of the shop.	480 hours

Cookie	Provider	Purpose	Expiry
ANONCHK	Microsoft (Clarity)	Auxiliary Microsoft cookies used to synchronise the identifier across its domains.	10 minutes
CLID	Microsoft (Clarity)	Identify the browser’s first visit to the website in Clarity.	1 year
MR	Microsoft (Clarity)	Auxiliary Microsoft cookies used to synchronise the identifier across its domains.	7 days
MUID	Microsoft (Clarity)	Identify unique browsers across Microsoft services.	1 year
SM	Microsoft (Clarity)	Auxiliary Microsoft cookies used to synchronise the identifier across its domains.	Session
_clck	Microsoft (Clarity)	Store Clarity’s pseudonymous identifier to recognise visits from the same browser.	1 year
_clsk	Microsoft (Clarity)	Group the pages viewed into the same Clarity session.	1 day

Auxiliary Batteries

Subcategories

How to identify and choose your 12V auxiliary battery

What the auxiliary or backup battery is for

Leading auxiliary battery brands

Compatibility and how to choose the right auxiliary

Frequently asked questions about auxiliary batteries

Best sellers in Auxiliary Batteries