Fulmen FK091 Start-Stop Auxiliary · Battery 9Ah 120A AGM

Yes. AGM (Absorbent Glass Mat) technology, 9 Ah and 12 V: sealed lead-acid, with the electrolyte held in glass fibre. Compared with a conventional battery it withstands more charge/discharge cycles and handles heat better; it is the required technology for cars with advanced Start-Stop and regenerative braking.

Yes: being AGM, the Fulmen FK091 is designed for Start-Stop cars. AGM batteries support advanced Start-Stop and regenerative braking thanks to their higher cycle count. Once fitted it is ready to go; registering it via OBD, advisable on most modern models, lets the alternator charge with the optimum profile. The general recommendation is EFB for basic Start-Stop and AGM where there is regenerative braking (it handles more cycles), unless the car manufacturer says otherwise.

As a guide, you can expect the Fulmen FK091 to last 5 to 8 years in mild-climate car use with Start-Stop, although the real figure may be higher or lower. What weighs most: temperature (cold makes starts harder and intense heat evaporates the electrolyte), frequent short trips, the condition of the alternator and charging system, power draw while parked and maintenance, not forgetting the type of car and Start-Stop.

Before buying, measure the space in your car: one extra millimetre can stop the hold-down clamp from closing. The Fulmen FK091 takes up 150×90×105 mm (length, width and height, terminals included).

On the Fulmen FK091, the polarity is positive on the left. To check, stand the battery in front of you with the terminals nearest you: the positive (+) is the one with the red ring. A change of polarity from the original means longer cables or a reconfigured system and can cause a short circuit: check it before ordering.

Three routes: the "Compatible vehicles" tab on this page, with the vehicles verified by our technical team; your number plate in the finder, from which DGT/DVLA/KBA detect model and engine; and WhatsApp, with make, model, engine and year, during business hours (Mon–Fri 10:00–13:30 and 16:30–18:00 (Spanish time, CET)). The FK091 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.

See the "Equivalents" section of this page for the recommended options at the same performance level. Mind the technology: in Start-Stop cars an EFB is not swapped for a conventional battery. Interchangeable means the same dimensions, same polarity, same Ah and same CCA; for the FK091, 9 Ah (120 A cranking).

Same case and same fitting as the FK091, from Exide. Compared with the FK091 it has the same Ah and cranking power. It costs €55.40 more. If you want to save or the FK091 is out of stock, it is the safe alternative: same dimensions, same polarity and official warranty.

Same case and same fitting as the FK091, from Tudor. Compared with the FK091 it has the same Ah and cranking power. It costs €61.70 more. If you want to save or the FK091 is out of stock, it is the safe alternative: same dimensions, same polarity and official warranty.

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. The Fulmen FK091 has a capacity of 9 Ah.

It is not strictly necessary on most cars, because the alternator detects the change and adapts the charge. The advisable step is to register it via OBD: the charging profile is optimum from the first minute and the battery lasts longer, especially on brands with sophisticated BMS (BMW, Mercedes, Audi, Volvo, Land Rover). Any garage with an OBD scanner can do it in a few minutes. If you prefer to do it yourself: VCDS / Carista (VAG), Bimmercode (BMW) or iCarsoft. Even if you do not register the Fulmen FK091, the car will start correctly; the profile adjusts within a few days.