# Marine battery Optima BTDC-4.2 12V 55Ah 765A AGM ![Marine battery Optima BTDC-4.2 12V 55Ah 765A AGM](https://baterias.com/845-home_default/battery-optima-blue-top-btdc-42-8016-253-12v-55ah.jpg) > Optima BTDC-4.2 marine battery 12V 55Ah 765A AGM. BLUE TOP range. Dimensions 254×175×200 mm, + terminal on the left. Cranking and house duties. **Category:** [Boat Batteries](https://baterias.com/gb/boat-batteries) → [OPTIMA](https://baterias.com/gb/optima) - **Canonical URL**: https://baterias.com/gb/battery-optima-blue-top-btdc-42-8016-253-12v-55ah - **Language**: en-GB - **Brand**: OPTIMA - **Reference**: BCOM-OPTIMA-BTDC-4.2 - **EAN**: 4016987113547 - **MPN**: BTDC-4.2 - **Price**: 216,90 € - **Stock**: In stock ## Technical specifications | Feature | Value | |---|---| | Brand | OPTIMA | | Reference | BTDC-4.2 | | Model | OPTIMA BLUE TOP | | Voltage (V) | 12 V | | Largo | 254 mm | | Ancho | 172 mm | | Alto | 173 mm | | Peso | 20.3 kg | | Tecnología | AGM ESPIRAL | | EAN | 4016987113547 | | Terminal layout | Positive terminal on the left | | Terminal type | 1 & 21 | | Cold cranking amps (EN) | 765 A | | Capacity (C20) | 55 Ah (c20) | | Capacity (C5) | 52 Ah (c5) | | ETN | 8162530008882 | ## Quick description **Optima BTDC-4.2 12V 55Ah 765A** is a marine battery, vibration- and deep-discharge resistant, suitable both for outboard engine starting and for onboard auxiliary services (navigation lights, GPS, sonar, fridge). Sealed and maintenance-free. ### Why this marine battery? - **Marine design** built for boat swell and vibration - **Dual function** starts the engine and powers onboard services - **Sealed and safe** maintenance-free even when the boat rolls 🔌 Voltage 12 V ⚡ Capacity 55 Ah C20 🔋 Cold cranking 765 A EN-1 📏 Dimensions 254×175×200 mm ⚙️ Technology AGM ESPIRAL 🧭 Polarity Positive on the left ⚖️ Weight 20,6 kg 🏷️ Model OPTIMA BLUE TOP ## Description ## Marine battery Optima BTDC-4.2 Blue Top 55Ah 765A 12V 12*V* Voltage 55*Ah* Capacity 765*A* Cold cranking 20.30*kg* Weight The **Optima BTDC-4.2** with spiral-cell AGM technology is a marine battery with **55 Ah** and **765 A** of cold cranking current (EN) for motor and sailing boats, both for engine starting and onboard services. It measures 254 × 172 × 173 mm and the positive terminal on the left, the format sought by anyone replacing a 55 Ah battery in boats. - Tolerates the daily cycling of a boat in season. - Powers onboard services: lights, sounder, GPS, fridge. - Reinforced case against vibration and swell. - Spiral cells: maximum vibration resistance and very powerful cranking. ### What the Optima BTDC-4.2 is for The Optima BTDC-4.2 is designed for motor and sailing boats, both for engine starting and onboard services. If it is your starter battery, run the services from a separate battery; if it is a service battery, avoid routinely discharging it beyond 50%. Check that it matches your current battery in dimensions, terminals and hold-down: this reference has a weight of 20.30 kg and 1 & 21 terminals. ### Dimensions, polarity and mounting In terms of format, the Optima BTDC-4.2 measures 254 × 172 × 173 mm (length × width × height) and weighs 20.30 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. Checking the three dimensions and the terminal position before buying avoids the most common mistake when replacing a battery. ### 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. We guarantee that every Optima arrives new, charged and with the manufacturer's full warranty. ### The Optima BTDC-4.2: Blue Top range and spiral-cell AGM technology The BTDC-4.2 is part of the Optima **Blue Top** range. Choosing the right reference within the series comes down to capacity, dimensions and terminals: technology and quality are common to the whole family. 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. ### How to make it last longer As a service battery, avoid routine discharges below 50% to extend its cycle life. Protect the terminals with dielectric grease and check the fixing: vibration and swell loosen connections. ### Manufacturer's warranty The Optima BTDC-4.2 comes with the **manufacturer's official warranty** against manufacturing defects. Deep discharge from winter lay-up without charging is not covered. ### 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 BTDC-4.2 an AGM battery and what are the benefits of AGM? Yes. The BTDC-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 boats with advanced Start-Stop and regenerative braking. Expected lifespan: 5-8 years under normal conditions. ### How do I change this battery step by step? In most boats 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 boats with Start-Stop or BMS, register the battery via OBD so the alternator applies the correct charging profile. ### How many years does this battery last? Expected lifespan of the Optima BTDC-4.2 is 5 to 8 years in mild-climate boat 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 measurements of the BTDC-4.2 model? 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 boat before buying: even one extra millimetre can prevent the hold-down clamp from closing. The height shown includes the terminals. ### What ETN and EAN codes does the Optima BTDC-4.2 battery have? The manufacturer reference (MPN) is BTDC-4.2 and its ETN code is 8162530008882 (short form 816 253 000), the European identifier used in spare-part catalogues. The EAN-13 barcode is 4016987113547. It belongs to the OPTIMA BLUE TOP range. Any of these codes identifies exactly this battery when requesting quotes or comparing prices. ### Is the BTDC-4.2 valid for my vehicle? 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 BTDC-4.2 typically fits a wide range of European vehicles thanks to its standard DIN case format. ### What are the equivalents of the BTDC-4.2 model? 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 boats. See the "Equivalents" section to view recommended options at the same performance level. ## Equivalent batteries - [OPTIMA BTSLI-4.2](https://baterias.com/gb/battery-optima-blue-top-btsli-42-8006-252-12v-50ah) ## Reviews - **Average rating**: 4.8 / 5 (36 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 · 2026-10-03*