# OPTIMA BLUE TOP batteries

> OPTIMA Blue Top marine AGM SpiralCell, dual terminal and moisture-resistant white case. 38-75 Ah, 730-900 A. BT R 3.7, BT S 4.2, BT D34M. Dispatched within 24h.

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## Description

**OPTIMA Blue Top batteries** are OPTIMA's marine AGM SpiralCell variant, with a dual marine terminal and a white case. 38-75 Ah, CCA 730-900 A, across the BT R 3.7, BT S 4.2, BT D34M and BT D31M models. Same technology as the Yellow Top, with marine hardware and an added auxiliary terminal.
Built for boats and leisure craft that need a reliable engine start and, on the higher-capacity models, enough power for onboard auxiliary loads (electronics, lights, fridge).

## OPTIMA Blue Top: SpiralCell for boating

The Blue Top series takes OPTIMA's SpiralCell technology — spiral-wound lead plates, high vibration resistance — and adapts it for the marine environment: white case, dual terminal (standard + auxiliary) for connecting chargers or solar panels, and better resistance to moisture and salt than a conventional lead-acid battery.

### Which Blue Top model your boat needs

- BT R 3.7 (44 Ah, 730 A): small motorboat.
- BT S 4.2 (55 Ah, 815 A): mid-size motorboat.
- BT D34M (55 Ah, 750 A): yacht or large runabout.
- BT D31M (75 Ah, 900 A): premium yacht with heavier auxiliary loads.

### Compatibility and how to choose

If your boat only needs engine starting, any Blue Top that fits the bay will do; if you also run electronics, a fridge or permanent lighting, step up to the D31M. For land use (car, motorcycle) the equivalent is the [Yellow Top](https://baterias.com/gb/batteries-optima-yellow-top). Confirm dimensions and terminals with our [battery comparator](https://baterias.com/gb/comparator).

## Frequently asked questions about OPTIMA Blue Top

### **What's the difference between Blue Top and Yellow Top?**

The internal technology is the same SpiralCell; the Blue Top adds a white case, dual marine terminal and better moisture resistance for boating.

### **Is it compatible with solar panels or an onboard charger?**

Yes, the Blue Top's auxiliary terminal is designed precisely for connecting chargers, solar panels or accessories without removing the main terminal.

### **How long does an OPTIMA Blue Top last on a boat?**

With correct maintenance (recharging after each trip, avoiding prolonged deep discharges) it typically lasts several boating seasons, longer than a conventional lead-acid battery in the same environment.

### **Do I need different Blue Tops for cranking and for loads?**

Not necessarily: the higher-capacity D34M and D31M models handle both engine cranking and moderate onboard auxiliary loads.

Catalogue curated by our technical team. **12,221 Trustpilot reviews · 4.5/5**. 24-48 h delivery in mainland Spain and Portugal (orders before 6:00 pm); 14-day returns with free collection on the Iberian mainland.

## Products in this category

| Product | Brand | Price |
|---|---|---|
| [Marine battery Optima BTDC-5.5 12V 75Ah 975A AGM](https://baterias.com/gb/battery-optima-blue-top-btdc-55-8052-188-12v-75ah) | OPTIMA | 263,70 € |
| [Marine battery Optima BTDC-4.2 12V 55Ah 765A AGM](https://baterias.com/gb/battery-optima-blue-top-btdc-42-8016-253-12v-55ah) | OPTIMA | 216,90 € |
| [Marine battery Optima BTSLI-4.2 12V 50Ah 815A AGM](https://baterias.com/gb/battery-optima-blue-top-btsli-42-8006-252-12v-50ah) | OPTIMA | 181,50 € |
| [Marine battery Optima BTDC-5.0 12V 66Ah 765A AGM](https://baterias.com/gb/battery-optima-blue-top-btdc-50-8027-227-12v-66ah) | OPTIMA | 225,70 € |

## 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 · 2026-10-27*