How long can a 12V 20Ah battery last at 100W?

[NatalieDella]

A 20Ah battery has approximately 0.2 kWh of electricity, which can power a 100W appliance for two hours. Additional information: 1. Working principle of 12V batteries: During charging, external electrical energy is used to regenerate the internal active materials, storing electrical energy as chemical energy. When discharging is needed, the chemical energy is converted back into electrical energy output, similar to commonly used mobile phone batteries in daily life. 2. Materials: It uses lead-based grids filled with sponge-like lead (also called grid bodies) as the negative electrode, lead-based grids filled with lead dioxide as the positive electrode, and dilute sulfuric acid with a density of 1.26-1.33g/ml as the electrolyte. When the battery discharges, metallic lead serves as the negative electrode, undergoing oxidation to form lead sulfate; lead dioxide serves as the positive electrode, undergoing reduction to form lead sulfate.

[Darlene]

You asked how long a 12V20Ah battery can power a 100W device. A simple theoretical calculation: 20 ampere-hours multiplied by 12 volts equals 240 watt-hours, divided by a 100W load gives 2.4 hours. But the real world isn't that ideal. Battery aging increases internal resistance, temperature extremes affect performance, and there are efficiency losses in charging equipment—for example, an inverter might only be 80% efficient. In reality, it might last just over 2 hours. If used in a car for lights or small appliances, never wait until it's fully depleted to stop. Deep discharging can damage the battery. It's advisable to stop at around 80% capacity; new batteries might fare slightly better. To extend usage, add a voltmeter to monitor the voltage. If it drops to 11.5 volts, stop immediately. Car batteries aren't toys—misuse could leave you stranded. Safety first.

[DelilahLee]

I have plenty of experience with car DIY projects. Using a 12V 20Ah battery to power a 100W load, such as speakers or LED lights, theoretically lasts 2.4 hours. However, in tests, a new battery might only last a little over 2 hours, while an old one could drop to around 1.5 hours. The reasons are simple: circuit losses, loose connections, and poor battery performance in cold weather. Additionally, avoid continuous heavy usage; give the battery intermittent breaks to recover some power, otherwise the voltage may drop sharply, making it hard to start the engine. It's best to have a backup power source or use the car's engine to assist with charging. In short, actual runtime is shorter than calculated, so plan carefully to avoid trouble on the road.

[ColeRose]

A 12V 20Ah battery driving a 100W device, basic calculation is 240Wh divided by 100W, resulting in 2.4 hours. But note the variables: poor battery health cuts time in half; high internal resistance or sulfation causes faster energy loss. Practically, choosing efficient devices like low-power inverters can extend runtime by 10%. Remember, deep discharging a car battery causes permanent damage, reducing capacity from 20Ah, making it harder to use later. Before use, test voltage and impedance—good habits prevent surprises. Simple maintenance: clean terminals to avoid corrosion, charge regularly.