A 300W inverter is typically used for small electronics such as: 300W ÷ 12V ≈ 25Ah After adding efficiency margin: Recommended battery: 12V 40Ah – 12V 50Ah For portable systems like camping or small backup power, a 12V lithium battery is usually the most efficient choice. In this guide, we'll explain what size battery you need for a 300W, 1000W, or 2000W inverter, and how to calculate the correct battery capacity for your system. An inverter converts DC power from a battery into AC power for household appliances. By inputting critical parameters such as power consumption, inverter efficiency, and desired usage time, this calculator provides a precise battery size. So I have made it easy for you, use the calculator below to calculate the battery size for 200 watt, 300 watt, 500 watt, 1000 watt, 2000 watt, 3000 watt, 5000-watt inverter Failed to calculate field. Battery capacity needed (Ah) = (Watts x Hours) / (Voltage x DOD x. Calculate exactly how many batteries you need for your power inverter setup. Compare runtime, voltage, efficiency, reserve, and bank design. Real watts from VA: watts = VA × power factor.