4WD Solar AU

Understanding 4WD Battery Runtime

How long will your 100Ah battery actually run your 12V fridge? Let's break down the math behind battery runtime.

The Basics: Amp Hours (Ah) vs. Watt Hours (Wh)

Most deep cycle batteries in Australia are rated in Amp Hours (Ah). To get Watt Hours (Wh), multiply Ah by the voltage (usually 12V). So, a 100Ah 12V battery holds 1200Wh of total energy.

Depth of Discharge (DoD)

You cannot use 100% of a battery's capacity without damaging it (unless it's Lithium).

  • AGM/Lead Acid: Safe DoD is 50%. A 100Ah battery gives you 50Ah of usable power.
  • Lithium (LiFePO4): Safe DoD is 80-100%. A 100Ah battery gives you 80-100Ah of usable power.

Calculating Your Load

A typical 40L compressor fridge (like an Engel or Waeco) might draw 1.5 to 2 amps per hour on average in the Australian heat. Over 24 hours, that's 36 to 48 Amp Hours.

The Easy Way

Instead of doing the math manually, use our 4WD Solar Calculator. It factors in your battery type, solar input, and average load to give you an accurate runtime estimation for your next outback trip.

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