# Fulmen FK091 · Auxiliary battery 12V 9Ah 120A

![Fulmen FK091 · Auxiliary battery 12V 9Ah 120A](https://bateriasonline.es/2678-home_default/fulmen-fk091.jpg)

> Fulmen FK091: 9 Ah auxiliary battery, 120 A (EN), 150×90×105 mm, positive terminal on the left, AGM. Equivalent to Exide EK091 and Tudor TK091.

**Category:** [Auxiliary batteries (back-up and in-vehicle service)](https://bateriasonline.es/en/auxiliary-backup-batteries) → [Fulmen](https://bateriasonline.es/en/fulmen-batteries)

- **Canonical URL**: https://bateriasonline.es/en/fulmen-fk091
- **Language**: en
- **Brand**: Fulmen
- **Reference**: BOL-FULMEN-FK091
- **EAN**: 3661024046336
- **MPN**: FK091
- **Last updated**: 2026-11-06

## Technical specifications

| Feature | Value |
|---|---|
| Brand | Fulmen |
| Range | FULMEN Start-Stop Auxiliary |
| Application | Auxiliary and back-up use |
| Technology | AGM |
| Voltage | 12 V |
| Capacity | 9 Ah |
| Cold cranking amps (EN) | 120 A |
| Length | 150 mm |
| Width | 90 mm |
| Height | 105 mm |
| Weight | 3.1 kg |
| Polarity | Positive terminal on the left |
| Terminal type | M12 |

## Quick description

The Fulmen FK091 is an auxiliary battery (AGM) with 12 V, 9 Ah and 120 A cold cranking current, measuring 150 × 90 × 105 mm, with the positive terminal on the left.

## Description

## The Fulmen FK091 at a glance

The Fulmen FK091 is an auxiliary vehicle battery: it powers back-up functions such as Start-Stop, electric steering or the emergency system while the main battery starts the engine. Without it, Start-Stop or back-up warnings appear on the dashboard.
The FK091 belongs to the Fulmen FULMEN Start-Stop Auxiliary range. [The full range of Fulmen batteries](https://bateriasonline.es/en/fulmen-batteries)

## Equivalents and alternatives to the Fulmen FK091

Other AGM batteries that fit the FK091's tray with the same polarity: an AGM can only be replaced by another AGM.

| Model | Technology | Capacity | Cold cranking (EN) | Dimensions (mm) |
|---|---|---|---|---|
| Exide EK091 | AGM | 9 Ah | 120 A | 150 × 90 × 105 |
| Tudor TK091 | AGM | 9 Ah | 120 A | 150 × 90 × 105 |
| Deta DK091 | AGM | 9 Ah | 120 A | 150 × 90 × 105 |
| Varta AUX9 | AGM | 9 Ah | 130 A | 151 × 87 × 106 |
| Kronobat AUX9 | AGM | 9 Ah | 130 A | 151 × 87 × 106 |
| Fulbat AUX9 | AGM | 8.4 Ah | – | 150 × 87 × 105 |

## Fulmen FK091 vs FK111

How the FK091 compares with Fulmen batteries of similar size and capacity:

| Model | Capacity | Cold cranking (EN) | Dimensions (mm) | Positive | Weight |
|---|---|---|---|---|---|
| Fulmen FK091 (this one) | 9 Ah | 120 A | 150 × 90 × 105 | left | 3.1 kg |
| Fulmen FK111 | 11 Ah | 150 A | 150 × 90 × 130 | left | 3.9 kg |

- Fulmen FK111: 2 Ah more, 30 A more cranking power, a different case (150 × 90 × 130 mm).

## What it means that the FK091 is AGM

The FK091 is AGM: the electrolyte is absorbed in glass fibre mats, so it is sealed and spill-proof. Being sealed, the FK091 can be fitted in the boot or under a seat with no risk of spills.

## What to look at before buying the FK091

- Measure the space: the FK091 takes up 150 × 90 × 105 mm.
- Polarity of the FK091: positive terminal on the left (if yours has it on the other side, the cables will not reach).
- Capacity of the FK091: 9 Ah; the same as your current battery or slightly more is fine.
- The FK091 delivers 120 A cold cranking (EN standard); do not go below what your original battery states.

## Part numbers and codes for the Fulmen FK091

Look for any of these FK091 codes on your current battery or in the manufacturer's catalogue:

| Commercial reference | FK091 |
|---|---|
| EAN | 3661024046336 |
| Terminal type | M12 |

## Frequently asked questions about the Fulmen FK091

### FK091 or FK111: which one suits me?

Compared with the FK091, the Fulmen FK111 has 2 Ah more and 30 A more cranking power. If your current battery says 150 A or more, choose the FK111; if it says 120 A or less, the FK091 is enough. Mind the space: the FK111 measures 150 × 90 × 130 mm.

### How much does the Fulmen FK091 weigh?

3.1 kg, with 9 Ah of capacity. For reference, the Fulmen FK111 (11 Ah) weighs 3.9 kg.

### Which battery is equivalent to the Fulmen FK091?

Only other AGM batteries with its dimensions and polarity: Exide EK091, Tudor TK091 and Deta DK091. Neither an EFB nor a conventional battery replaces the FK091.

### Which side is the positive terminal on the Fulmen FK091?

On the FK091, 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.

## Keep comparing: alternatives to the FK091

- [More auxiliary batteries (back-up and in-vehicle service)](https://bateriasonline.es/en/auxiliary-backup-batteries)
- [Full Fulmen catalogue](https://bateriasonline.es/en/fulmen-batteries)
- [Exide EK091](https://bateriasonline.es/en/exide-ek091) · 9 Ah, 120 A, 150×90×105 mm
- [Tudor TK091](https://bateriasonline.es/en/tudor-tk091) · 9 Ah, 120 A, 150×90×105 mm

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