Fulbat AUX12 Auxiliary AGM · Auxiliary battery 10.5Ah

Yes, it is AGM. In an AGM battery such as the AUX12, the electrolyte is not free but absorbed in a glass-fibre mat inside a sealed lead-acid battery. Its advantages: more charge/discharge cycles than a conventional battery and better heat tolerance. It is also required in cars with advanced Start-Stop and regenerative braking.

AGM batteries support advanced Start-Stop and regenerative braking thanks to their higher cycle count. The Fulbat AUX12 is AGM, so yes, it is designed for Start-Stop cars. It works once fitted; on most modern cars, registering it via OBD is advisable so the alternator applies the optimum charging profile. As a rule: EFB for basic Start-Stop, AGM when there is also regenerative braking (more cycles); in any case, what the car manufacturer specifies.

As a rough estimate, the Fulbat AUX12 typically lasts 5 to 8 years in mild-climate car use with Start-Stop; it is a guide figure, not a guaranteed period. Actual lifespan varies with climate (cold starts, heat evaporating the electrolyte), with usage and short journeys, with the condition of the alternator and charging system, with power draw while parked and with maintenance; the type of car and Start-Stop also count.

Before buying, measure the space in your car: one extra millimetre can stop the hold-down clamp from closing. The Fulbat AUX12 takes up 150×87×130 mm (length, width and height, terminals included).

Polarity of the Fulbat AUX12: positive on the left. Seen from the front, terminals towards you, the positive (+) is the post with the red ring. Compare it with the battery you are replacing: if it does not match, cables must be lengthened or the system reconfigured, with a risk of short circuit.

The quickest way is to enter your number plate in the finder: DGT/DVLA/KBA detect model and engine. You can also look at the "Compatible vehicles" tab, verified by our technical team, or send us make, model, engine and year on WhatsApp; we answer during business hours (Mon–Fri 10:00–13:30 and 16:30–18:00 (Spanish time, CET)). The AUX12 typically fits a wide range of European vehicles thanks to its standard DIN case format. The car manufacturer's specifications always take priority over our tables.

Not just any technology will do: an EFB cannot be replaced with a conventional battery in Start-Stop cars. The "Equivalents" section further down lists the recommended alternatives. A direct equivalent needs what this AUX12 offers: 150×87×130 mm, positive on the left, the same Ah and CCA and AGM technology.

The absorbent glass-fibre mat of an AGM retains the electrolyte, so it cannot leak and withstands considerably more cycles than a conventional battery. Hence it is recommended for advanced Start-Stop with regenerative braking, such as BMW EfficientDynamics, Mercedes Eco, Audi MHEV, Land Rover ECO or Volvo i-Stop, and it handles tilting, vibration and extreme temperatures better than an EFB.

Advisable, yes; essential, on most cars, no. Registering it via OBD makes the alternator charge with the optimum profile from the first minute and extends battery life, which matters most on brands with sophisticated BMS such as BMW, Mercedes, Audi, Volvo or Land Rover. Without registration there is no starting problem: the alternator adjusts the profile within a few days. A workshop only needs an OBD scanner and a few minutes. DIY apps: VCDS / Carista (VAG), Bimmercode (BMW), iCarsoft.