How to Set Up an External Fridge for Your Travel Trailer (Without Killing Your Battery)

The Basics: Why External Fridges Drain Batteries

A 12V compressor fridge is one of the biggest constant power draws in a travel trailer setup. Unlike lights or a phone charger that you use briefly, a fridge runs 24 hours a day, cycling on and off to maintain temperature.

A typical 90L dual zone fridge draws 0.8–1.2 Ah per hour on average. Over 24 hours, that is 19–29 Ah — a significant chunk of most travel trailer battery setups.

Battery Sizing Guide

Rule of thumb

You need enough usable battery capacity to run the fridge overnight (12–14 hours) without other charging sources, plus a safety margin.

For a 90L dual zone fridge (approx 1.0 Ah/h average):

What most RVers run

• Budget setup: Single 120Ah AGM — tight, but works with solar backup
• Comfortable setup: 200Ah lithium — handles fridge plus lights, charging, and a fan
• Overkill (but nice): 300Ah+ lithium — run everything without thinking about it

Solar Requirements

Solar panels recharge your batteries during the day so they can power the fridge overnight.

Minimum solar for a 90L fridge:

• 200W panel: Adequate in summer, may struggle in winter or overcast conditions
• 300W panel: Comfortable year-round in most of Australia
• 400W+ panels: Handles the fridge plus other loads without stress

Key factors

• Panel angle and orientation matter more than raw wattage in winter
• Shade on even one cell can dramatically reduce output
• An MPPT solar controller is significantly more efficient than PWM

Wiring Your External Fridge

Anderson plug setup (most common)

1. Run a dedicated circuit from your battery to an Anderson plug mounted externally
2. Use minimum 6mm² (13.5mm² for longer runs over 3m) twin core cable
3. Install a 15A fuse or circuit breaker at the battery end
4. Mount the Anderson plug where your fridge slide sits

Key wiring tips

• Keep cable runs short — voltage drop over long thin cables wastes energy and can cause compressor issues
• Use quality Anderson plugs — cheap copies have higher resistance and can overheat
• Add a low voltage disconnect — protects your starter battery if the auxiliary runs flat. Most modern fridges have built-in low voltage cutoff, but an external one adds a safety layer
• Avoid running through the cigarette lighter socket — these are limited to 10–15A and the connections are unreliable for constant loads

Fridge Placement Tips

On a fridge slide

• Ensure the slide is rated for the loaded weight (fridge + contents = 40–50kg)
• Allow ventilation clearance around the compressor (usually at the back)
• Secure the fridge to the slide with straps or bolts — it will move on corrugated roads

Inside the travel trailer

• Provide airflow around the compressor — heat buildup reduces efficiency
• Consider a fan to circulate air around the unit in hot weather
• Factor the weight into your travel trailer's rear payload if it is behind the axle

Tips to Reduce Power Draw

1. Pre-cool the fridge on 240V before leaving home — it uses far less power to maintain temperature than to cool down from ambient
2. Keep it in shade — direct sun on the fridge body forces the compressor to work harder
3. Minimise lid openings — every open lets warm air in. Know what you want before you open it
4. Pack it full — a full fridge holds temperature better than a half-empty one. Fill gaps with bottles of water
5. Set realistic temperatures — fridge at 3–5°C and freezer at -15°C to -18°C. Colder than necessary wastes power

Weight Considerations

A 90L fridge adds significant weight to your setup:

Use KamperHub's weight calculator to factor this into your travel trailer payload. If the fridge sits on an external slide at the rear, it also affects your tongue weight and weight distribution.

The Bottom Line

An external fridge is one of the best upgrades for travel trailer travel — no more ice runs, no soggy food, and cold drinks whenever you want them. Get the battery and solar sizing right, wire it properly, and it will run reliably for years.

Useful Resources

• Dometic — Product Support
• Engel — Portable Fridge Range

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KamperHub Team

Helping travellers tow safely and confidently. KamperHub provides tools for trip planning, weight compliance, and adventure management.