# Fulbat AUX9 · Auxiliary battery 12V 8.4Ah

![Fulbat AUX9 · Auxiliary battery 12V 8.4Ah](https://bateriasonline.es/583-home_default/fulbat-aux9.jpg)

> Fulbat AUX9: 8.4 Ah auxiliary battery, 150×87×105 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) → [Fulbat](https://bateriasonline.es/en/fulbat-batteries)

- **Canonical URL**: https://bateriasonline.es/en/fulbat-aux9
- **Language**: en
- **Brand**: Fulbat
- **Reference**: BOL-FULBAT-AUX9
- **MPN**: AUX9
- **Last updated**: 2026-11-06

## Technical specifications

| Feature | Value |
|---|---|
| Brand | Fulbat |
| Range | FULBAT Auxiliary AGM |
| Application | Auxiliary and back-up use |
| Technology | AGM |
| Voltage | 12 V |
| Capacity | 8.4 Ah |
| Length | 150 mm |
| Width | 87 mm |
| Height | 105 mm |
| Polarity | Positive terminal on the left |

## Quick description

The Fulbat AUX9 is an auxiliary battery (AGM) with 12 V and 8.4 Ah, measuring 150 × 87 × 105 mm, with the positive terminal on the left.

## Description

## Where the Fulbat AUX9 fits

The Fulbat AUX9 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 AUX9 belongs to the Fulbat FULBAT Auxiliary AGM range. [More Fulbat batteries](https://bateriasonline.es/en/fulbat-batteries)

## Equivalents and alternatives to the Fulbat AUX9

Other AGM batteries that fit the AUX9's tray with the same polarity: an AGM can only be replaced by another AGM.

| Model | Technology | Capacity | Dimensions (mm) |
|---|---|---|---|
| Varta AUX9 | AGM | 9 Ah | 151 × 87 × 106 |
| Kronobat AUX9 | AGM | 9 Ah | 151 × 87 × 106 |
| Exide EK091 | AGM | 9 Ah | 150 × 90 × 105 |
| Tudor TK091 | AGM | 9 Ah | 150 × 90 × 105 |
| Fulmen FK091 | AGM | 9 Ah | 150 × 90 × 105 |
| Deta DK091 | AGM | 9 Ah | 150 × 90 × 105 |

## Fulbat AUX9 vs AUX12

How the AUX9 compares with Fulbat batteries of similar size and capacity:

| Model | Capacity | Dimensions (mm) | Positive |
|---|---|---|---|
| Fulbat AUX9 (this one) | 8.4 Ah | 150 × 87 × 105 | left |
| Fulbat AUX12 | 10.5 Ah | 150 × 87 × 130 | left |

- Fulbat AUX12: 2.10 Ah more, a different height (130 mm instead of 105 mm). It only fits if there is room for 130 mm of height.

## AGM technology in the AUX9

The AUX9 is AGM: the electrolyte is absorbed in glass fibre mats, so it is sealed and spill-proof. Being sealed, the AUX9 can be fitted in the boot or under a seat with no risk of spills.

## What to look at before buying the AUX9

- The AUX9 needs 150 × 87 × 105 mm of space: measure it with the hold-down clamp in place.
- The AUX9 has the positive terminal on the left: compare it with your current battery.
- With 8.4 Ah, the AUX9 replaces an original battery of that capacity or slightly less.

## Frequently asked questions about the Fulbat AUX9

### Fulbat AUX9 or AUX12: what changes?

Mainly the height: the AUX9 is 105 mm tall and the Fulbat AUX12 130 mm, with the same length and width and 10.5 Ah against 8.4 Ah. Before choosing between the AUX9 and the AUX12, measure the free height of the battery compartment with the cover or bonnet closed.

### Which battery is equivalent to the Fulbat AUX9?

Only other AGM batteries with its dimensions and polarity: Varta AUX9, Kronobat AUX9 and Exide EK091. Neither an EFB nor a conventional battery replaces the AUX9.

### Which side is the positive terminal on the Fulbat AUX9?

On the AUX9, 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.

### What warnings does the car give when the auxiliary battery fails?

Typically Start-Stop unavailable, back-up battery fault or emergency call system fault. The car still starts, but those functions are disabled.

## Keep comparing: alternatives to the AUX9

- [Other auxiliary batteries (back-up and in-vehicle service)](https://bateriasonline.es/en/auxiliary-backup-batteries)
- [More Fulbat models](https://bateriasonline.es/en/fulbat-batteries)
- [Varta AUX9](https://bateriasonline.es/en/varta-aux9) · 9 Ah, 130 A, 151×87×106 mm
- [Kronobat AUX9](https://bateriasonline.es/en/kronobat-aux9) · 9 Ah, 130 A, 151×87×106 mm

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