EXIDE AUXILIARY

The auxiliary battery: electrical backup for modern cars

The auxiliary battery (or backup battery) is a small AGM unit independent of the main battery: it keeps the electronics and safety systems powered while the main battery is busy cranking the engine or Start-Stop keeps it switched off. Being sealed AGM, it can sit inside the cabin or boot with no risk of leaks or gases, and it needs no maintenance. Like any battery it loses capacity over the years — and the car flags it on the dashboard.

Exide auxiliary battery models

• Exide EK112 — 12 Ah: auxiliary battery for the Mercedes E-Class and BMW 5 Series.
• Exide EK113 — 13 Ah: auxiliary battery for the Mercedes S-Class and BMW 7 Series.
• Exide EK120 — 20 Ah: backup battery for 48 V mild-hybrid systems.

How to identify your car's auxiliary battery

Find the reference on the auxiliary battery itself (usually under the boot floor, under a seat or next to the main battery) and compare it with each Exide EK data sheet. You can also check the batteries compatible with your car in our battery comparator, and if in doubt our technical team will confirm the exact reference.

Frequently asked questions about auxiliary car batteries

What is the auxiliary battery in a car?

A small second battery, typically a 12-20 Ah AGM, that backs up the main one: it keeps the electronics and safety systems powered during engine cranking and Start-Stop pauses.

What does the auxiliary battery malfunction warning mean?

That the auxiliary battery has reached the end of its life and no longer holds enough charge. The car keeps running on the main battery, but it should be replaced soon so you do not lose functions.

Can I keep driving with a faulty auxiliary battery?

Generally yes, temporarily: the main battery takes over the work. But Start-Stop and some comfort or assistance functions may be disabled until the new auxiliary battery is fitted.

What is the difference between the main battery and the auxiliary one?

The main battery (60-105 Ah) cranks the engine and powers the whole vehicle; the auxiliary (12-20 Ah) is a dedicated backup for the electronics. They are not interchangeable: each has its own slot and reference.

Catalogue curated by our technical team. 12,030 Trustpilot reviews · 4.5/5. 24-48 h delivery in mainland Spain and Portugal (orders before 6:00 pm); 14-day returns with free collection on the Iberian mainland.