# Car battery Optima RTU-4.2 12V 50Ah 815A AGM ![Car battery Optima RTU-4.2 12V 50Ah 815A AGM](https://baterias.com/833-home_default/battery-optima-red-top-rtu-42-8004-250-12v-50ah.jpg) > Optima RTU-4.2 car battery 12V 50Ah 815A AGM. RED TOP range. Dimensions 254×175×200 mm, + terminal on the left. Check fitment by plate. **Category:** [Car Batteries](https://baterias.com/gb/car-batteries) → [OPTIMA](https://baterias.com/gb/optima) - **Canonical URL**: https://baterias.com/gb/battery-optima-red-top-rtu-42-8004-250-12v-50ah - **Language**: en-GB - **Brand**: OPTIMA - **Reference**: BCOM-OPTIMA-RTU-4.2 - **EAN**: 4016987113486 - **MPN**: RTU-4.2 - **Price**: 185,80 € - **Stock**: In stock ## Technical specifications | Feature | Value | |---|---| | Brand | OPTIMA | | Reference | RTU-4.2 | | Model | OPTIMA RED TOP | | Voltage (V) | 12 V | | Largo | 254 mm | | Ancho | 172 mm | | Alto | 173 mm | | Peso | 18 kg | | Tecnología | AGM ESPIRAL | | EAN | 4016987113486 | | Terminal layout | Positive terminal on the left | | Terminal type | 1 & 21 | | Cold cranking amps (EN) | 815 A | | Capacity (C20) | 50 Ah (c20) | | ETN | 8042500008882 | ## Quick description **Optima RTU-4.2 12V 50Ah 815A** is a ready-to-use passenger car battery, sealed and maintenance-free. Delivers the cranking amps the engine needs in cold weather and keeps stable voltage for modern car loads (ECU, sensors, climate control, infotainment). ## Why this car battery? - **Original-equipment quality** without dealership prices - **Lasts 4 to 6 years** buy once instead of twice - **Real human tech support** if you have any doubts before buying 🔌 Voltage 12 V ⚡ Capacity 50 Ah C20 🔋 Cold cranking 815 A EN-1 📏 Dimensions 254×175×200 mm ⚙️ Technology AGM ESPIRAL 🧭 Polarity Positive on the left ⚖️ Weight 18,4 kg 🏷️ Model OPTIMA RED TOP ## Description ## Car battery Optima RTU-4.2 Red Top 50Ah 815A 12V 12*V* Voltage 50*Ah* Capacity 815*A* Cold cranking 18*kg* Weight The **Optima RTU-4.2** from the **Red Top** range delivers **50 Ah** and **815 A** of cold cranking current (EN) at **12 V**: the usual specification for passenger cars with conventional starting, without a Start-Stop system. Measuring 254 × 172 × 173 mm and the positive terminal on the left, it is the direct replacement for cars fitted from the factory with a 50 Ah battery of this format. - Low self-discharge: copes with long stops without losing charge. - Designed to last several years under normal daily use. - Spiral AGM construction, sealed and mountable in any position. - Stable voltage for the vehicle electronics (ECU, sensors, climate control). ### What the Optima RTU-4.2 is for With 50 Ah, the Optima RTU-4.2 is sized for passenger cars with conventional starting, without a Start-Stop system. It is a direct replacement for the original battery as long as dimensions and terminals match. Check that it matches your current battery in dimensions, terminals and hold-down: this reference has a weight of 18 kg and 1 & 21 terminals. ### Will it fit your current battery tray? It has external dimensions of 254 × 172 × 173 mm and weighs 18 kg. The positive terminal on the left decides which side the cables end up on: it is the detail that causes most buying mistakes, so check it before ordering. It uses 1 & 21 terminals, the system that anchors and connects it in the vehicle. Before replacing it, measure your current battery tray: if all three dimensions and the terminal positions match, the swap is direct and needs no adapters. ### The Optima RTU-4.2: Red Top range and spiral-cell AGM technology The **Red Top** is the Optima range the RTU-4.2 belongs to: it shares the same construction and quality criteria with the rest of the series, and varies in capacity and format to suit each vehicle. In a spiral-cell battery the electrolyte is absorbed and the plates are wound under pressure. That lets it deliver very high current peaks, recharge quickly and be mounted in any position. ### Why choose Optima batteries The Optima Red, Yellow and Blue Top are references for high-performance starting, deep cycling and marine use respectively, all with the characteristic six spiral-cell design. At baterias.com we work directly with the manufacturer or its official distributor: real stock, brand-new product and official warranty. ### Manufacturer's warranty The Optima RTU-4.2 comes with the **manufacturer's official warranty** against manufacturing defects; the exact period is stated in the brand's conditions. If it fails through a defect within the period, we replace it free of charge. ### How to make it last longer Avoid leaving lights or accessories on with the engine off: most batteries fail not through defects but through repeated deep discharges. Charge with a voltage-controlled AGM charger; a fully discharged pure-lead battery may need a specific charger to recover. ### Shipping, delivery and returns Order **before [[ks:cutoff]]** with stock available and it leaves today: mainland Spain and Portugal receive it in 24-48 working hours, the islands and the rest of the EU in 3 to 5 days. You have **[[ks:return_days]] days** to return it if it has not been installed, with free collection on the mainland, and shipment tracking by email. ## Frequently asked questions ### Is the Optima RTU-4.2 an AGM battery and what are the benefits of AGM? Yes. The RTU-4.2 from Optima uses AGM (Absorbent Glass Mat) technology: a sealed lead-acid battery where the electrolyte is absorbed in a glass-fibre mat. It withstands more charge/discharge cycles than a conventional one, handles heat better and is the required technology for cars with advanced Start-Stop and regenerative braking. Expected lifespan: 5-8 years under normal conditions. ### Is the Optima RTU-4.2 battery suitable for Start-Stop? Yes. As AGM technology it is designed for Start-Stop vehicles. AGM batteries support advanced Start-Stop and regenerative braking thanks to their higher cycle count. EFB is recommended for basic Start-Stop; AGM is recommended when regenerative braking is also present, thanks to its higher cycle capability. It works straight out of the box — on most modern vehicles registering the battery via OBD is recommended so the alternator automatically applies the optimal charging profile. ### How is the Optima RTU-4.2 battery installed in the vehicle? In most cars it fits in 15-30 minutes with a 10 mm wrench; if the battery is under the seat or in the boot the time can double. See the step-by-step guide on this page. Quick summary: 1) switch off the engine and remove the key; 2) locate the original battery (engine bay, boot or under seat); 3) disconnect the negative (−) terminal first, then the positive (+); 4) loosen the hold-down clamp and remove the old battery; 5) fit the new one in the same orientation — match the polarity shown on the product sheet; 6) connect the positive (+) first, then the negative (−). On cars with Start-Stop or BMS, register the battery via OBD so the alternator applies the correct charging profile. ### What is the service life of the RTU-4.2 model? Expected lifespan of the Optima RTU-4.2 is 5 to 8 years in mild-climate car use with Start-Stop. In cold regions it drops slightly due to cold-start stress; in very hot regions it also drops because of electrolyte evaporation. To extend its life: avoid deep discharges (headlights on with engine off), have the alternator checked yearly, and keep the battery clean and properly secured. ### What are the dimensions of the Optima RTU-4.2 battery? Dimensions (length × width × height) are 254×175×200 mm — also written as 254x175x200 mm — following the European DIN standard. Always measure the space in your car before buying: even one extra millimetre can prevent the hold-down clamp from closing. The height shown includes the terminals. ### Under which reference is the Optima RTU-4.2 listed in catalogues? The manufacturer reference (MPN) is RTU-4.2 and its ETN code is 8042500008882 (short form 804 250 000), the European identifier used in spare-part catalogues. The EAN-13 barcode is 4016987113486. It belongs to the OPTIMA RED TOP range. Any of these codes identifies exactly this battery when requesting quotes or comparing prices. ### Does this battery fit my car? Three options to confirm: 1) enter your number plate in the finder (DGT/DVLA/KBA auto-detect your model and engine); 2) check the "Compatible vehicles" tab on this page, where we list every vehicle verified by our technical team; 3) if you cannot find your model, message us on WhatsApp with brand, model, engine and year — we reply during business hours (Mon–Fri 10:00–13:30 and 16:40–18:00 (Spanish time, CET)). The RTU-4.2 typically fits a wide range of European vehicles thanks to its standard DIN case format. ### Which batteries are equivalent to the Optima RTU-4.2? Directly interchangeable batteries (same dimensions, same polarity, same Ah and CCA) are the OEM equivalents from leading brands: Bosch, Tudor, Exide and, depending on the model, Banner or Yuasa. Exact equivalence depends on technology — an EFB cannot be replaced with a conventional battery in Start-Stop cars. See the "Equivalents" section to view recommended options at the same performance level. ### Why choose AGM instead of EFB for my Start-Stop car? AGM (Absorbent Glass Mat) technology uses absorbent fibreglass that retains the electrolyte, eliminating leaks and allowing up to 3× more charge/discharge cycles than a conventional battery. It is the recommended option when the car has advanced Start-Stop with regenerative braking (BMW EfficientDynamics, Mercedes Eco, Audi MHEV, Land Rover ECO, Volvo i-Stop). Withstands tilted positions, high vibration and extreme temperatures better than EFB. The Optima RTU-4.2 is fully original and meets European EN 50342-6 standards for advanced Start-Stop. ### Do I need to register the Optima RTU-4.2 on the car after installation? On most cars it is not strictly necessary — the alternator detects the new battery and adapts the charge automatically. It is recommended to register the battery via OBD so that the alternator applies the optimal charging profile from the first minute and extends the battery life as much as possible (especially on brands with sophisticated BMS: BMW, Mercedes, Audi, Volvo, Land Rover). Any workshop with an OBD scanner (~10-15 € labour) does it in 5 minutes. DIY apps: VCDS / Carista (VAG), Bimmercode (BMW), iCarsoft. If you do not register, the car will still start correctly — the alternator just takes a few days to adjust the profile. The Optima RTU-4.2 ships factory-charged at 80-90% so you can use it straight after fitting. ## Reviews - **Average rating**: 4.84 / 5 (38 reviews) ## Technical team (editorial authorship) The FAQs, guides and comparisons on this site are reviewed by the baterias.com technical team — over 25 years of experience validating automotive batteries. → https://baterias.com/gb/technical-team --- *baterias.com — Automotive batteries · 2026-10-05*