Optima RTC-4.2 Red Top · Car battery 50Ah 815A AGM

Yes. AGM (Absorbent Glass Mat) technology, 50 Ah and 12 V: sealed lead-acid, with the electrolyte held in glass fibre. It is the technology required by cars with advanced Start-Stop and regenerative braking. It withstands more cycles than a conventional battery and copes better with heat.

AGM batteries support advanced Start-Stop and regenerative braking thanks to their higher cycle count. The Optima RTC-4.2 is AGM, so yes, it is designed for Start-Stop cars. 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.

Allow 15-30 minutes and a 10 mm spanner. If the car keeps its battery in the boot or under a seat, it can take up to twice as long. For the detail, read our guide to replacing the car battery and, if in doubt, the owner's handbook or a main dealer. 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, keeping the polarity; reconnect the positive (+) first and the negative (−) last.

As a rough estimate, the Optima RTC-4.2 typically lasts 5 to 8 years in mild-climate car use with Start-Stop; it is a guide figure, not a guaranteed period. It can vary considerably with usage (short or long journeys), temperature, the condition of the alternator and charging system, power drawn with the engine off and maintenance, plus the car itself and Start-Stop. Cold demands more at every start and intense heat evaporates the electrolyte.

Check the room available in your car, because a single millimetre too much can stop the clamp from closing. Its dimensions are 254×175×200 mm, also written 254x175x200 mm; the height already includes the terminals.

Its EAN-13 barcode is 4016987113455. The ETN, the European identifier in parts catalogues, is 8012870008882, also written 801 287 000; and the manufacturer's reference is RTC-4.2. It belongs to the OPTIMA RED TOP range. Any of them pins down this exact battery.

Not sure? Try your number plate in the finder (DGT/DVLA/KBA detect model and engine) or the "Compatible vehicles" tab, checked by our technical team; if your car is not there, send us make, model, engine and year on WhatsApp and we will reply 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 compatibility list for the RTC-4.2 runs to 12 verified vehicle versions.

A direct equivalent needs what this RTC-4.2 offers: 254×175×200 mm, the same Ah and CCA and AGM technology. 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.

Same case and same technology as the RTC-4.2: an alternative by size, not an official equivalent. Compared with the RTC-4.2 it has the same Ah and cranking power. It costs 1,60 € more. If the polarity matches and your car had a similar capacity, it works as a replacement; if in doubt, ask us with your model.

It has the same dimensions, voltage and technology as the RTC-4.2, although it is not a manufacturer-approved equivalent. Compared with the RTC-4.2 it has the same Ah and cranking power. It costs 24,10 € more. Check the positive terminal side and the original capacity before ordering; otherwise it is a straight swap.

Cold cranking current (EN) of the Optima RTC-4.2: 815 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. For regenerative braking systems such as BMW EfficientDynamics, Mercedes Eco, Audi MHEV, Land Rover ECO or Volvo i-Stop, AGM is the recommendation; it also copes better than an EFB with tilting, vibration and extreme temperatures.

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. Without registration the car starts normally; the alternator simply takes a few days to adjust the profile. Any workshop with an OBD scanner does it in a few minutes; DIY, with VCDS or Carista (VAG group), Bimmercode (BMW) or iCarsoft.