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

Yes, it is AGM. In an AGM battery such as the RTR-4.2, the electrolyte is not free but absorbed in a glass-fibre mat inside a sealed lead-acid battery. 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 Optima RTR-4.2 is designed for Start-Stop cars. AGM batteries support advanced Start-Stop and regenerative braking thanks to their higher cycle count. It needs nothing to work, though on most modern cars registering it via OBD is advisable so the alternator adjusts its charging profile. 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.

If the car manufacturer lists any extra step in the handbook, follow it. More detail in how to replace the car battery. 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. What matters most is the terminal order: removing, negative (−) before positive (+); refitting, positive (+) before negative (−). In between, with the engine off and the key out, release the clamp and fit the new battery the same way round as the original, positive on the right (polarity).

As a guide, you can expect the Optima RTR-4.2 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 Optima RTR-4.2 takes up 254×175×200 mm (length, width and height, terminals included), with a B11 hold-down.

On the Optima RTR-4.2, the polarity is positive on the right. It must match your current battery: reversed polarity means lengthening cables or reconfiguring the system, with a risk of short circuit. To check, stand the battery in front of you with the terminals nearest you: the positive (+) is the one with the red ring.

Its EAN-13 barcode is 4016987113479. The ETN, the European identifier in parts catalogues, is 8032510008882, also written 803 251 000; and the manufacturer's reference is RTR-4.2. It belongs to the OPTIMA RED TOP range. Any of them pins down this exact battery.

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)). According to our data, 37 verified vehicle versions are compatible with the RTR-4.2. The car manufacturer's specifications always take priority over our tables.

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

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

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). The absorbent glass-fibre mat of an AGM retains the electrolyte, so it cannot leak and withstands considerably more cycles than a conventional battery. Cold cranking current (EN) of the Optima RTR-4.2: 815 A.

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. If you do not register the RTR-4.2, it will keep starting fine while the alternator adjusts the profile over a few days.