How Many Hours Can Your Battery Run? + Calculator Explained

Link to the calculator: https://cleversolarpower.com/battery-... 🎁 Free Diagrams: https://cleversolarpower.com 📖 My Best-Selling book on Amazon: https://cleversolarpower.com/off-grid... Calculating your battery runtime is easier than you think. In this video, I’ll walk you through two methods: one simple and quick, and another more advanced and accurate. Plus, I’ll introduce a free calculator I developed to make the process even easier. We start with the easy method. The first step is determining the usable capacity of your battery. This is done by multiplying the voltage of the battery by its amp-hour capacity. For a lead-acid battery, the calculation would be 12V * 100Ah = 1200Wh. However, lead-acid batteries should only be discharged to 50% to extend their lifespan, so the usable capacity is actually 600Wh. For a lithium battery, which has a nominal voltage of 12.8V, the same calculation gives 1,280Wh. Unlike lead-acid, lithium batteries can be discharged up to 100% without significantly affecting their lifespan. With most lithium batteries rated for 6,000 cycles, you can safely use their full capacity without concern. Once we know the usable capacity, we simply divide by the power consumption of an appliance. If we have a 60W TV, we calculate the runtime for lead-acid as 600Wh / 60W = 10 hours. For lithium, we get 1,280Wh / 60W = 21 hours. That’s the easy method. Now, let’s look at the more advanced method. The advanced method accounts for efficiency losses in the battery and inverter. A lead-acid battery is about 85% efficient, meaning 15% of energy is lost as heat. Adjusting for this, our lead-acid usable capacity is 600Wh * 0.85 = 510Wh. If the TV is running on an inverter, which is typically 90% efficient, we divide the power consumption by 0.9, making the adjusted power usage 67W. Our new runtime is now 510Wh / 67W = 7.6 hours, less than the previously calculated 10 hours. The same process applies to lithium batteries, which are 95% efficient. This makes the new usable capacity 1,280Wh * 0.95 = 1,216Wh. Keeping the inverter efficiency the same, the TV still consumes 67W, leading to a new runtime of 1,216Wh / 67W = 18 hours, slightly lower than the previous 21-hour estimate. This method is much more accurate. If you don’t want to do all these calculations manually, my free tool can help. I’ll walk you through how it works. First, you select your battery type—lead-acid or lithium—then enter the voltage and capacity. Next, you add your appliances. There’s a difference between AC and DC devices, as AC devices must account for inverter losses. For example, adding a 60W TV running for 4 hours and a 40W laptop running for 3 hours automatically adjusts for efficiency losses. You can also add DC loads like LED lights, which are not affected by inverter losses. The tool then calculates total AC and DC consumption and provides an estimated runtime. For example, in this case, the runtime might be around 5 hours. If you want to add a fridge, my tool allows for compressor cycling, so instead of running continuously, you can enter an estimated duty cycle, such as 30% of the time. For a fridge that consumes 80W, this means entering 8 hours of actual runtime per day, giving a much more accurate estimate.