Battery Life Calculator

If you’re running a solar powered system, whether it’s for a caravan, campervan, RV, or an off grid cabin, knowing how long your batteries will last under load is critical. Overestimating or underestimating your battery life can leave you stranded without power or result in overspending on unnecessary battery capacity. This is exactly why we created our Battery Life Calculator!

Tip: Feel Free to use our energy usage calculator to work out your total load power.

How Our Solar Battery Runtime Calculator Works

Our Solar 12V to 48V Battery Runtime Calculator estimates how long your battery will last based on electrical principles used in off grid system design.

Step 1: Enter Battery Capacity (Ah)

Input the amp-hour (Ah) rating of your battery or total battery bank.

Step 2: Enter Battery Voltage (V)

• A typical 12V battery has a nominal voltage of 12.8V
• A typical 24V battery has a nominal voltage of 25.6V
• A typical 48V battery has a nominal voltage of 52.2V

Tip: You could measure the battery voltage using a voltmeter and enter that value

Step 3: Enter Total Load Power (W)

Enter the total wattage of all appliances running at the same time.

What Is Battery Runtime?

Battery runtime is the length of time your battery can supply power to your loads before it is depleted to a safe level.

It depends on three main factors:

• Battery capacity (Ah): How much energy your battery can store
• Nominal battery voltage (V): 12.8V, 25.6V , or 51.2V
• Load power (W): The total wattage of appliances running

Battery chemistry and system losses also play a major role in determining usable energy.

Why Battery Runtime Matters in Off-Grid Solar Systems

Your battery is the heart of your off-grid energy system. It stores energy from your solar panels and supplies power when there is no sunlight.

Knowing your battery runtime helps you:

• Avoid running out of power overnight or during poor weather
• Protect your batteries from excessive discharge
• Size your battery bank correctly
• Design a reliable and cost effective solar system

Battery capacity alone doesn’t tell the full story, runtime depends on how quickly energy is being used.

How Battery Runtime Is Calculated

We calculate the battery runtime by first working out the battery’s available energy (in Wh) as:

Battery Energy (Wh) = Battery Capacity (Ah) × Battery Voltage (V)

We then calculate the usable capacity based on the battery type to avoid fully discharging your battery and damaging it:

• A Lithium battery has ~80% usable capacity
• A Lead acid / AGM has ~50% usable capacity

A small loss factor of 10% is also included to account for inverter losses and system inefficiencies.

Finally, the runtime is calculated as:

Battery Runtime (hours) = Usable Battery Energy (Wh) ÷ Load Power (W)

This provides a realistic runtime estimate for off-grid systems.

Benefits of Using a Battery Runtime Calculator

Using our battery runtime calculator helps you:

• Protect battery health by avoiding deep discharge
• Plan energy usage more effectively
• Compare lithium vs lead acid performance easily

Tips for More Accurate Results

For best results, keep the following in mind:

• Use real appliance power consumption, not just the nameplate ratings by measuring current and voltage in the circuit
• Add together all the appliances running at the same time
• Lead-acid batteries perform worse at high loads compared to lithium
• Cold temperatures can reduce available battery capacity

The calculator provides a realistic estimate, but real world conditions may vary slightly. You could also find more useful information in our complete guide about leisure batteries for Caravans, Camper Vans and Motorhomes