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

Yes. The Optima RTR-3.7 is AGM (Absorbent Glass Mat): sealed lead-acid, with the electrolyte absorbed 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.

Yes. It is a AGM battery of 44 Ah, designed for vehicles with Start-Stop. AGM batteries support advanced Start-Stop and regenerative braking thanks to their higher cycle count. Registering it via OBD is advisable on most modern cars (the alternator then applies the optimum profile), but it works from the start. 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.

Tool: a 10 mm spanner. Time: 15-30 minutes on almost every car, and up to double if the battery is not under the bonnet but in the boot or under a seat. 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 right), keeping the polarity; reconnect the positive (+) first and the negative (−) last.

Estimated lifespan of the Optima RTR-3.7: 5 to 8 years in mild-climate car use with Start-Stop. Treat it as an approximate guide, as every case is different. 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.

The RTR-3.7 has the positive on the right: that is its polarity. If your current battery has its positive on the other side, this one is not suitable without longer cables or a reconfigured system (short-circuit risk). Face the battery with its terminals nearest you and see which side the positive post (+, red ring) is on.

Parts catalogues list it under ETN 835 255 000 (in full, 8352550008882); the manufacturer's reference is RTR-3.7 and its EAN-13 is 4016987113578. 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)). According to our data, 2 verified vehicle versions are compatible with the RTR-3.7. Always cross-check with what the car manufacturer states in the owner's handbook.

Technology matters too: in Start-Stop cars, an EFB cannot be replaced with a conventional battery. The options at the same level are in the "Equivalents" section of this page. A direct equivalent needs what this RTR-3.7 offers: 237×172×197 mm, positive on the right, the same Ah and CCA and AGM technology.

It is the bigger sister of the RTR-3.7 in the same Optima range. Compared with the RTR-3.7 it has 4 Ah more and 70 A of cold cranking less. It costs 11,90 € more. If the tray takes the size, extra reserve never hurts; for a daily-driven petrol car the extra is not needed.

Cold cranking current (EN) of the Optima RTR-3.7: 730 A. 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. Compared with an EFB it resists tilted positions, heavy vibration and extreme temperatures better, and it is the recommended option where there is regenerative braking (BMW EfficientDynamics, Mercedes Eco, Audi MHEV, Land Rover ECO, Volvo i-Stop).

On most cars it is not strictly necessary: the alternator detects the new battery and adapts the charge by itself. It is advisable, though, to register it via OBD so the optimum profile applies from the first minute and the battery lasts as long as possible, especially on brands with sophisticated BMS (BMW, Mercedes, Audi, Volvo, Land Rover). Without registration the car starts normally; the alternator simply takes a few days to adjust the profile. To do it yourself: VCDS or Carista on VAG, Bimmercode on BMW, iCarsoft. At a workshop with an OBD scanner it takes minutes.