Marine battery Optima BTDC-4.2 12V 55Ah 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.

Three ways: 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 for the BTDC-4.2; 3) if you cannot find your model, message us on WhatsApp with brand, model, engine and year — we reply during business hours (Mon–Fri 9:00–18:00 CET).

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.

We provide 2 years of official manufacturer warranty against manufacturing defects. It applies to defects such as damaged cells, internal short-circuits or abnormal capacity loss. Wear from misuse (prolonged overcharging, wrong charger or faulty alternator) is not covered. Once the defect is verified by technical inspection, we replace the BTDC-4.2 at no cost.

In mainland Spain and Portugal it arrives in 24 h if you order before 17:00 and the battery is in stock — it leaves the same day and arrives the next business day. Afternoon or weekend orders ship the next business day. For Balearics, Canaries and other EU destinations, allow 2-5 days. Shipping cost is calculated in the cart based on destination and service (standard, express, cash on delivery). Tracking number is sent by email + SMS as soon as the parcel ships.

Yes. You have 14 days from delivery to return it. In mainland Spain and Portugal returns are FREE — we cover the return shipping cost via prepaid label. In other EU countries the return shipping cost is the customer's. It must arrive in its original packaging with no signs of installation. If it was defective, the warranty covers replacement even after the 14-day period.

The current price at baterias.com is €178.70 (VAT included), updated every 24 hours. Shipping cost is calculated in the cart based on destination and chosen service (standard, express, cash on delivery). If you find it cheaper elsewhere (same product and same delivery time), message us on WhatsApp and we will match the price.

At baterias.com — authorised distributor with real stock, 24h delivery in mainland Spain and Portugal if you order before 17:00, and full manufacturer warranty. Shipping cost is calculated in the cart based on destination and chosen service (standard, express, cash on delivery). Secure payment by card, Bizum, PayPal or bank transfer. If you choose at-home installation, our technician will take the used battery and dispose of it through an authorised collection point.

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.

Dimensions (length × width × height) are 254×172×173 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.

It weighs 20,3 kg. Most of the weight is lead. If you plan to fit it yourself, use gloves and a carrying strap (AGM batteries are slightly heavier than conventional due to the absorbent glass-mat fibre).

Nominal capacity 55 Ah[?cca: and [cold-cranking amps 765 A]] at 12 V. Ah measure the total energy available (autonomy); CCA (also written A in cold or EN under the European standard) measure the instantaneous power to crank the starter motor. A battery with more CCA starts better in winter; one with more Ah keeps accessories on for longer.

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 9:00–18:00 CET). The BTDC-4.2 typically fits a wide range of European vehicles thanks to its standard DIN case format.

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.

This battery and its equivalents from Bosch, Tudor or Exide are technically comparable: same dimensions, same voltage and same capacity. The differences are warranty (Varta and Bosch: 2 years; Tudor and Exide: 2 years on the equivalent line), manufacturing plant (Varta and Bosch share origin in the Clarios Group; Tudor and Exide belong to Stryten Energy) and price. For private use any of these brands will give 4-6 years of life. Compare them in the "Equivalents" section.

The average rating of the Optima BTDC-4.2 on baterias.com is 4.8/5 from 27 verified customer reviews. The product rating, when available, is shown above and in the "Reviews" section. You can also check our public Trustpilot profile at shop level (4.4/5 from 10,354+ verified reviews). Most-praised points: reliable cold start, lifespan above 5 years and fast delivery; most common complaints mention BMS-equipped boats that need OBD registration after fitting.