# Marine battery Optima BTSLI-4.2 12V 50Ah 815A AGM

![Marine battery Optima BTSLI-4.2 12V 50Ah 815A AGM](https://baterias.com/3808-home_default/battery-optima-blue-top-btsli-42-8006-252-12v-50ah.jpg)

> Optima BTSLI-4.2 marine battery 12V 50Ah 815A 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-btsli-42-8006-252-12v-50ah
- **Language**: en-GB
- **Brand**: OPTIMA
- **Reference**: BCOM-OPTIMA-BTSLI-4.2
- **EAN**: 4016987113493
- **MPN**: BTSLI-4.2
- **Price**: 181,50 €
- **Stock**: In stock

## Technical specifications

| Feature | Value |
|---|---|
| Brand | OPTIMA |
| Reference | BTSLI-4.2 |
| Model | OPTIMA BLUE TOP |
| Voltage (V) | 12 V |
| Largo | 254 mm |
| Ancho | 172 mm |
| Alto | 173 mm |
| Peso | 18 kg |
| Tecnología | AGM ESPIRAL |
| EAN | 4016987113493 |
| Terminal layout | Positive terminal on the left |
| Terminal type | 1 & 21 |
| Cold cranking amps (EN) | 815 A |
| Capacity (C20) | 50 Ah (c20) |
| ETN | 8062520008882 |

## Quick description

**Optima BTSLI-4.2 12V 50Ah 815A** is a marine battery with reinforced anti-vibration case for moorings and offshore use. Tolerates the typical daily cycles on a boat (engine start + night-time services such as lights, sonar, fridge) and holds voltage even when the hull is rolling in open sea.

## 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
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 BLUE TOP

## Description

## Marine battery Optima BTSLI-4.2 Blue Top 50Ah 815A 12V

12*V* Voltage
50*Ah* Capacity
815*A* Cold cranking
18*kg* Weight

The **Optima BTSLI-4.2 marine battery** offers **12 V**, **50 Ah** and **815 A** of cold cranking current (EN) from the **Blue Top** range with spiral-cell AGM technology, designed for motor and sailing boats, both for engine starting and onboard services. Measuring 254 × 172 × 173 mm and the positive terminal on the left, it is the direct replacement for boats fitted from the factory with a 50 Ah battery of this format.
- Sealed: no spills or gases in the locker.
- Resistant to humidity and salt air.
- Spiral AGM construction, sealed and mountable in any position.
- Ready for starting outboard and inboard engines.

### Vehicles compatible with the Optima BTSLI-4.2

The Optima BTSLI-4.2 is compatible with more than 58 vehicles: it is fitted as original equipment or as a replacement by brands such as Fendt, Deutz-Fahr, New Holland, Ford, International-Harvester and Inter Harv.. It is a go-to option when you need a **battery for a Fendt**, Deutz-Fahr or other models that use this same format. Models from Isuzu and Jeep are added to that list.

### Dimensions, polarity and mounting

The Optima BTSLI-4.2 is made in the 254 × 172 × 173 mm format 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. Checking the three dimensions and the terminal position before buying avoids the most common mistake when replacing a battery.

### What Optima does differently

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. All the Optima batteries in our catalogue are genuine product, recently manufactured and covered by the manufacturer's warranty.

### The Optima BTSLI-4.2: Blue Top range and spiral-cell AGM technology

Within the Optima catalogue, the **Blue Top** series groups the references designed for this use. The BTSLI-4.2 is the 50 Ah model of that family, with the same performance as its siblings in other sizes.
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. Charge with a voltage-controlled AGM charger; a fully discharged pure-lead battery may need a specific charger to recover.

### Manufacturer's warranty

The Optima BTSLI-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

Orders placed **before [[ks:cutoff]]** with the battery in stock ship the same day. Delivery in mainland Spain and Portugal takes 24-48 working hours; for the Balearic Islands and the rest of the European Union allow 3 to 5 working days. You have **[[ks:return_days]] days** to return an unused battery; in mainland Spain and Portugal collection is free. We email you the tracking number as soon as the parcel ships.

## Frequently asked questions

### Is the Optima BTSLI-4.2 an AGM battery and what are the benefits of AGM?

Yes. The BTSLI-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 our blog. 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 — with positive on the left 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 BTSLI-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 dimensions of the Optima BTSLI-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 boat before buying: even one extra millimetre can prevent the hold-down clamp from closing. The height shown includes the terminals.

### Which side is the positive terminal on this battery?

Polarity: positive on the left. To identify it, place the battery in front of you with the terminals facing you and check which side the positive (+, marked with a red ring) is on. Before buying, verify the polarity matches your current battery: switching polarity forces longer cables or system reconfiguration, with short-circuit risk.

### What ETN and EAN codes does the Optima BTSLI-4.2 battery have?

The manufacturer reference (MPN) is BTSLI-4.2 and its ETN code is 8062520008882 (short form 806 252 000), the European identifier used in spare-part catalogues. The EAN-13 barcode is 4016987113493. It belongs to the OPTIMA BLUE TOP range. Any of these codes identifies exactly this battery when requesting quotes or comparing prices.

### Will the Optima BTSLI-4.2 battery fit my boat?

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 BTSLI-4.2 fits 30 verified vehicle versions in our database.

### Which batteries are equivalent to the Optima BTSLI-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 boats. See the "Equivalents" section to view recommended options at the same performance level.


## Compatible vehicles

This battery fits 30 vehicles. Most searched:

- [FENDT Farmer (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/fendt/farmer)
- [FENDT Favorit (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/fendt/favorit)
- [DEUTZ-FAHR Agrotron (1995)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/deutz-fahr/agrotron)
- [FENDT GT (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/fendt/gt)
- [ISUZU FORWARD F (1990)](https://baterias.com/gb/batteries-for-truck/isuzu/forward-f)
- [DEUTZ-FAHR Agroplus (1996)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/deutz-fahr/agroplus)
- [DEUTZ-FAHR Agrolux (2000)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/deutz-fahr/agrolux)
- [FORD 5000-Serie (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/ford/5000-serie)
- [NEW HOLLAND WORKMASTER (2009)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/new-holland/workmaster)
- [NEW HOLLAND Series T4 POWERSTAR (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/new-holland/series-t4-powerstar)
- [INTERNATIONAL-HARVESTER C-Series (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/international-harvester/c-series)
- [INTERNATIONAL-HARVESTER CM-Series (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/international-harvester/cm-series)
- [INTER HARV. CM-Series (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/inter-harv/cm-series)
- [JEEP PATRIOT (MK74) (2007)](https://baterias.com/gb/car-batteries/jeep/patriot-mk74)
- [FORD 6000-Serie (1990)](https://baterias.com/gb/batteries-for-construction-and-agricultural-machinery/ford/6000-serie)

## Equivalent batteries

- [OPTIMA BTDC-4.2](https://baterias.com/gb/battery-optima-blue-top-btdc-42-8016-253-12v-55ah)

## Reviews

- **Average rating**: 5 / 5 (1 reviews)

## Technical team (editorial authorship)

The FAQs, guides and comparisons on this site are reviewed by the baterias.com technical team — automotive battery specialists since 2012.

→ https://baterias.com/gb/technical-team

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*baterias.com — Automotive batteries · 2026-10-21*