Ultra Slim Lithium Battery

$1,390.00$6,050.00 inc. GST

Upgrade your vehicle with our Ultra Slim lithium auxiliary battery, available in 8 capacities from 100Ah to 620Ah. The sleek design allows flexible installation in 4x4s, utes, vans and canopies. Suitable for just about any 12V auxiliary power need.

Built for rugged locations and extreme Aussie terrain, these high-capacity auxiliary batteries deliver top performance to power all your gear, ensuring reliable power wherever your going.

Add Welded Side Mounted Rail Kit to your 280ah or 310ah Ultra Slim Battery

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Australian Made

Made in Brisbane, you can depend on our top-notch quality and rugged performance.

Designed by Enthusiasts

Designed by our team of off-roading and camping enthusiasts, our auxiliary battery systems are perfect to power your adventure.


Product 100Ah 200Ah 280Ah 310Ah 400Ah 450Ah 550Ah 620Ah
BMS Constant Discharge 180 AMP 200 AMP 330 AMP 380 AMP
Peak Discharge 700 AMPs 850 AMPs 1800 AMPs
Constant Charge 50 AMPs 100 AMPs
Peak Charge 100 AMPs 200 AMPs
Nominal Voltage 12.8v
Length 490mm 580mm
Width 300mm 370mm
Height 55mm 60mm 82mm 110mm 115mm
Weight 14 kg 22 kg 25 kg 38 kg 58 kg
Operating Temp -20°C – 60°C
Terminals M8 terminals M10 terminals
Charge Voltage 14.2v – 14.6v
Absorption/float 13.4v – 13.6v
Cut off voltage 10.5v



Equip your vehicle with a Custom Lithium Ultra Slim auxiliary battery. Designed to fit anywhere and deliver the highest battery capacity to power all your gear for longer.


Can I swap out my AGM battery for an Ultra Slim Lithium Battery?

The possibility of swapping your AGM battery for an Ultra Slim Lithium Battery primarily depends on your current charging setup. AGM and lithium batteries have distinct charging cycles and chemical properties. Lithium batteries, while lighter and more efficient with a longer lifespan, require more precise charging profiles to prevent damaging the battery, to prevent overcharging and avoid potential safety hazards.

Before proceeding with a swap, it’s crucial to verify that your existing chargers and related equipment are compatible with lithium batteries. Ensure to consult the manuals for your DC-DC charger, solar charge controller, and 240V charger, among others. These should support the specific needs of lithium batteries to facilitate a safe and effective transition from AGM to lithium technology.

How do I restart my flat Ultra Slim lithium auxiliary battery?

There are two main methods to restart an Ultra Slim Lithium Battery that has run flat:

Method 1: The simplest method involves using a lithium-compatible 240V charger with a ‘power supply’ mode. Connect the Ultra Slim Lithium Battery to the charger, set it to ‘power supply’ mode, and allow it to charge until full. This method helps wake up the battery and continue charging.

Method 2: If you do not have access to a 240V charger, you can restart your battery using another 12V battery with similar voltage and capacity:

  • Equip yourself with jumper leads with positive and negative clamps.
  • Position the two batteries next to each other, ensuring they do not touch.
  • Connect the positive clamp of the jumper leads to the positive terminal of both batteries.
  • Connect the negative clamp to the negative terminal of both batteries.
  • Activate the vehicle or power source equipped with a DC-DC charger to start the charge.
  • Once charging is confirmed, carefully disconnect the jumper leads, starting with the negative.

If your Ultra Slim Lithium Battery remains unresponsive after an extended discharge period, it may require servicing. Please return it to Custom Lithium for professional assessment. It is highly recommended to fully charge the battery after a successful reset to ensure optimal performance.

What size DCDC charger would I need for my Ultra Slim Lithium Battery?

All the DC-DC chargers we offer are fully compatible with our Ultra Slim Lithium Batteries. Whether you choose a charger with a built-in MPPT solar regulator or a straightforward DC-DC charger, you’ll find an option that suits your needs.

The choice between smaller and larger DCDC charger models largely depends on your desired charging speed. For our larger Ultra Slim Lithium Batteries, we recommend opting for a larger DC-DC charger to ensure more efficient recharging. However, even our smaller batteries can handle a robust 40A charger for quicker charging. Alternatively, using a smaller DCDC charger, such as 25A or 30A, is also viable but expect slower charging times.

If you are considering a charger from a third party or planning to use an existing one, make sure the lithium DCDC charger is configured to support a 13.4 ~ 13.6 volts absorption/float charge and a bulk charge of 14.2 ~ 14.6 volts to ensure optimal charging performance and battery health.

What 12V Charge Profile is required for the Ultra Slim?

For optimal performance of the Ultra Slim Lithium Battery, specific charging parameters need to be adhered to. The battery requires a charge voltage between 14.2V and 14.6V for effective charging. The absorption and float voltage should be maintained between 13.4V and 13.6V to ensure the battery is charged safely without risking overcharge.

The cutoff voltage for these batteries is set at 10.5V, protecting against excessive discharge and potential damage. Depending on the model, the charging current capacity varies: the 100Ah model supports a standard charge current of 50A and a maximum of 100A, while larger models ranging from 200Ah to 620Ah can handle a standard charge current of 100A and a maximum of 200A.

If your charger, like the Victron 12-12/30, offers a LiFePO4 setting, it’s advised to use this option to align with the battery’s requirements. This setting ensures that the charger outputs the correct voltage profile and maximizes the battery’s performance and longevity.

These guidelines are designed to ensure that your Ultra Slim Lithium Battery operates at peak efficiency, providing reliable and sustained power under various conditions.

Additional information

Weight 14 kg
Dimensions 490 × 300 × 55 mm
Capacity Size

100Ah Ultra Slim, 200Ah Ultra Slim, 280Ah Ultra Slim, 310Ah Ultra Slim, 400Ah Ultra Slim, 450Ah Ultra Slim, 550Ah Ultra Slim, 620Ah Ultra Slim