# Optima BTDC-4.2 · Boat battery 12V 55Ah 765A

![Optima BTDC-4.2 · Boat battery 12V 55Ah 765A](https://bateriasonline.es/12-home_default/optima-btdc-4-2.jpg)

> Optima BTDC-4.2 (ETN 816253000): 55 Ah boat battery, 765 A (EN), 254×175×200 mm, positive terminal on the left, spiral AGM.

**Category:** [Marine and boat batteries](https://bateriasonline.es/en/marine-boat-batteries) → [Optima](https://bateriasonline.es/en/optima-batteries)

- **Canonical URL**: https://bateriasonline.es/en/optima-btdc-4-2
- **Language**: en
- **Brand**: Optima
- **Reference**: BOL-OPTIMA-BTDC-4.2
- **EAN**: 4016987113547
- **MPN**: BTDC-4.2
- **Price**: 212,24 € (VAT incl., Spain)
- **Last updated**: 2026-11-06

## Technical specifications

| Feature | Value |
|---|---|
| Brand | Optima |
| Range | OPTIMA BLUE TOP |
| Application | Boats |
| Technology | Spiral AGM |
| Voltage | 12 V |
| Capacity | 55 Ah |
| Cold cranking amps (EN) | 765 A |
| Length | 254 mm |
| Width | 175 mm |
| Height | 200 mm |
| Weight | 20.6 kg |
| Polarity | Positive terminal on the left |
| Terminal type | 1 & 21 |
| ETN code | 816253000 |

## Quick description

Optima BTDC-4.2 (ETN 816 253 000, also written 816253000): boat battery with 12 V, 55 Ah and 765 A cold cranking current, measuring 254 × 175 × 200 mm, with the positive terminal on the left.

## Description

## Who the Optima BTDC-4.2 is for

The Optima BTDC-4.2 is made for marine use. Check whether your boat needs starting, service or a dual-purpose battery before choosing.
The BTDC-4.2 belongs to the Optima OPTIMA BLUE TOP range. [The full range of Optima batteries](https://bateriasonline.es/en/optima-batteries)

## Spiral AGM technology in the BTDC-4.2

Inside, the BTDC-4.2 rolls its plates into cylindrical cells (spiral AGM). It is the basis of OPTIMA batteries.

## Optima BTDC-4.2 vs BTSLI-4.2 and BTDC-5.0

The real differences between the BTDC-4.2 and the closest Optima models:

| Model | Capacity | Cold cranking (EN) | Dimensions (mm) | Positive | Weight |
|---|---|---|---|---|---|
| Optima BTDC-4.2 (this one) | 55 Ah | 765 A | 254 × 175 × 200 | left | 20.6 kg |
| Optima BTSLI-4.2 | 50 Ah | 815 A | 254 × 175 × 200 | left | 18.4 kg |
| Optima BTDC-5.0 | 66 Ah | 765 A | 309 × 172 × 221 | left | 24.4 kg |

- Optima BTSLI-4.2: 5 Ah less, 50 A more cranking power, the same dimensions.
- Optima BTDC-5.0: 11 Ah more, the same cranking power, a different case (309 × 172 × 221 mm).

## Equivalents and alternatives to the Optima BTDC-4.2

We have no other battery with exactly the dimensions and polarity of the BTDC-4.2. Browse the rest of our [marine and boat batteries](https://bateriasonline.es/en/marine-boat-batteries) to compare close options.

## Part numbers and codes for the Optima BTDC-4.2

This is how the Optima BTDC-4.2 appears on the label and in parts catalogues:

| Commercial reference | BTDC-4.2 |
|---|---|
| ETN code | 816253000 (also 816 253 000) |
| EAN | 4016987113547 |
| Case size according to Optima | 34 (BCI) |
| Base hold-down | B00 |
| Terminal type | 1 & 21 |
| Also known as | Optima 816253000 · Optima 816 253 000 |

## What to look at before buying the BTDC-4.2

- Check the EN amps on your battery: if it says 765 A or less, the BTDC-4.2 covers your engine.
- Capacity of the BTDC-4.2: 55 Ah; the same as your current battery or slightly more is fine.
- Polarity of the BTDC-4.2: positive terminal on the left (if yours has it on the other side, the cables will not reach).
- Measure the space: the BTDC-4.2 takes up 254 × 175 × 200 mm.

## Frequently asked questions about the Optima BTDC-4.2

### BTDC-4.2 or BTSLI-4.2: which one suits me?

Compared with the BTDC-4.2, the Optima BTSLI-4.2 has 5 Ah less and 50 A more cranking power. If your current battery says 815 A or more, choose the BTSLI-4.2; if it says 765 A or less, the BTDC-4.2 is enough. Both measure 254 × 175 × 200 mm, so they fit the same tray.

### What is the ETN code of the Optima BTDC-4.2?

816253000, also written 816 253 000. The ETN (European Type Number) is printed on the label and used in parts catalogues.

### How much does the Optima BTDC-4.2 weigh?

20.6 kg, with 55 Ah of capacity. For reference, the Optima BTSLI-4.2 (50 Ah) weighs 18.4 kg.

### Which side is the positive terminal on the Optima BTDC-4.2?

On the BTDC-4.2, the positive terminal is on the left with the terminals facing you: compare it with your current battery, because with reversed polarity the cables will not reach.

### Which charger does the Optima BTDC-4.2 need?

A charger with an AGM mode. If the battery has dropped below 10.5 V some chargers will not recognise it: use one with a recovery mode or one specific to spiral AGM.

## More batteries to compare with the BTDC-4.2

- [More marine and boat batteries](https://bateriasonline.es/en/marine-boat-batteries)
- [The whole Optima range](https://bateriasonline.es/en/optima-batteries)

---
*bateriasonline.es — Batteries and accessories · 2026-11-10*