Tudor TK091 Auxiliar · Auxiliary battery 9Ah 120A AGM

Yes: the TK091 from Tudor uses AGM (Absorbent Glass Mat) technology, a sealed lead-acid battery whose electrolyte soaks a glass-fibre mat. 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 Tudor TK091 is AGM, so yes, it is designed for Start-Stop cars. It needs nothing to work, though on most modern cars registering it via OBD is advisable so the alternator adjusts its charging 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 rough estimate, the Tudor TK091 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 Tudor TK091 takes up 150×90×105 mm (length, width and height, terminals included).

Polarity of the Tudor TK091: positive on the left. It must match your current battery: reversed polarity means lengthening cables or reconfiguring the system, with a risk of short circuit. Seen from the front, terminals towards you, the positive (+) is the post with the red ring.

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 car manufacturer's specifications always take priority over our tables. The TK091 typically fits a wide range of European vehicles thanks to its standard DIN case format.

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. To replace the Tudor TK091 without modifications, the other battery must be identical in size, polarity, Ah and CCA.

The Exide alternative that fits where the TK091 goes, with the same polarity. Compared with the TK091 it has the same Ah and cranking power. It costs 6,30 € less. A straight swap with nothing to adapt; the difference is the price and the brand you prefer.

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. This TK091 delivers 120 A cold cranking (EN).

The alternator detects the new battery and adapts the charge automatically, so on most cars it is not compulsory. Even so, it is advisable to register it via OBD so charging is optimum from the first minute and the battery lasts longer, particularly on BMW, Mercedes, Audi, Volvo or Land Rover, with more sophisticated BMS. Any workshop with an OBD scanner does it in a few minutes; DIY, with VCDS or Carista (VAG group), Bimmercode (BMW) or iCarsoft. If you do not register the TK091, it will keep starting fine while the alternator adjusts the profile over a few days.