Optima RTU-3.7 Red Top · Car battery 44Ah 730A AGM

Yes. AGM (Absorbent Glass Mat) technology, 44 Ah and 12 V: sealed lead-acid, with the electrolyte held in glass fibre. 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 Optima RTU-3.7 is AGM, so yes, it is designed for Start-Stop cars. 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.

On most cars it is a 15-30 minute job needing only a 10 mm spanner (up to twice as long when the battery is under a seat or in the boot). Before you start, check the car handbook: the manufacturer's procedure always comes first. Our full step-by-step guide is on the blog. The right order: engine off and key out; disconnect the negative (−) first, then the positive (+); release the hold-down clamp, lift out the old battery and seat the new one in the same position (positive on the left), keeping the polarity; reconnect the positive (+) first and the negative (−) last.

As a rough estimate, the Optima RTU-3.7 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.

Check the room available in your car, because a single millimetre too much can stop the clamp from closing. Its dimensions are 237×172×197 mm, also written 237x172x197 mm; the height already includes the terminals.

Polarity of the Optima RTU-3.7: positive on the left. Seen from the front, terminals towards you, the positive (+) is the post 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.

Parts catalogues list it under ETN 822 255 000 (in full, 8222550008882); the manufacturer's reference is RTU-3.7 and its EAN-13 is 4016987113561. It belongs to the OPTIMA RED TOP range. Any of the three works for getting a quote or comparing prices without mix-ups.

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)). Always cross-check with what the car manufacturer states in the owner's handbook. The RTU-3.7 fits 37 verified vehicle versions in our database.

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. A direct equivalent needs what this RTU-3.7 offers: 237×172×197 mm, positive on the left, the same Ah and CCA and AGM technology.

It has the same dimensions, voltage and technology as the RTU-3.7, although it is not a manufacturer-approved equivalent. Compared with the RTU-3.7 it has the same Ah and cranking power. It costs 3,50 € more. Check the positive terminal side and the original capacity before ordering; otherwise it is a straight swap.

In an AGM (Absorbent Glass Mat) battery the electrolyte is held in a glass-fibre mat: no spills, and many more charge/discharge 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. Cold cranking current (EN) of the Optima RTU-3.7: 730 A.

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 RTU-3.7, it will keep starting fine while the alternator adjusts the profile over a few days.