How Long Will A 12v Battery Run A 400 Watt Inverter?

Are you curious about how long will a 12V battery run a 400 watt inverter? Well, you've come to the right place!

Determining the runtime of a 12V battery on a 400W inverter involves considering various factors. Let's break it down step by step:

An easy solution: Use our battery runtime calculator.

Calculate How Long Will A 12v Battery Run a 400 Watt Inverter

Step 1: Convert Battery Ah to Watt-hours (Wh)

First, let's calculate the battery capacity in watt-hours. Use this formula:

Battery capacity in watt-hours = Battery amp-hours (Ah) × Battery Volts. 

For example, if you have a 12V 50Ah battery, the calculation would be:

50Ah × 12V = 600 watt-hours.

Step 2: Consider the battery discharge efficiency

Different battery types have varying discharge efficiencies. Based on data:

  • Lead-acid batteries: Discharge efficiency ≈ 80-85%
  • Lithium-ion batteries: Discharge efficiency ≈ 90-95%

Suppose you have a 12V 50Ah lead-acid battery. Applying the discharge efficiency, the calculation would be:

600 × 0.85 = 510 watt-hours

Step 3: Apply Depth of Discharge (DoD) Limit

Each battery type has a recommended DoD limit:

  • Lead-acid, AGM, and gel batteries: ≈ 50% DoD
  • Lithium (LiFePO4) batteries: ≈ 100% DoD

Considering a lead-acid battery, after applying the DoD limit, the calculation would be:

Battery capacity in Wh after DoD limit = 510 × 50% = 255 usbale Wh.

Step 4: Consider Inverter Efficiency

Most inverters have an efficiency rate of around 90%. To account for this, the calculation would be:

Battery AC watts = 255 × 90% = 230 AC watt-hours.

Step 5: Determine Runtime

Divide the battery AC watt-hours by the total load connected. Assuming a 400-watt appliance connected to your 50Ah battery, the calculation would be:

230 ÷ 400 = 0.5 hours or 35 minutes

It turns out, a 12V 50Ah lead-acid battery will last 35 minutes on a 400-watt inverter.

Factors affecting 12v battery runtime on 400 watt inverter

While these calculations provide estimates, it's important to consider certain factors that can affect battery runtime:

  1. Battery Life Cycle Count: Over time, the storage capacity of a battery decreases with each charging and discharging cycle. This can impact the actual runtime, so it's essential to consider the number of cycles the battery has undergone.
  2. Batteries Are Rated for 5 Amps Over 20 Hours: Lead-acid batteries are designed for a 20-hour discharge period, ideally at a rate of 5 amps. Discharging batteries at higher rates can generate heat and result in power loss, which the provided methods may not account for. Check the battery's discharge rate specified by the manufacturer.

How Long Will a 12V Battery Last with a 400 Watt Inverter?

To give you a clear idea of estimated battery runtime, here's a chart showcasing the expected runtime for different 12V battery capacities and types when powering a 400W inverter:

12V Battery CapacityBattery TypeEst. Runtime
50AhLead-acid40 minutes
60AhLead-acid48 minutes
70AhLead-acid1 hour
100AhLead-acid1.3 hours
150AhLead-acid2 hours
200AhLead-acid2.7 hours
50AhLithium (LiFePO4)1.3 hours
60AhLithium (LiFePO4)1.6 hours
70AhLithium (LiFePO4)1.9 hours
100AhLithium (LiFePO4)2.7 hours
150AhLithium (LiFePO4)4 hours
200AhLithium (LiFePO4)5.4 hours


  • A 12V lead-acid battery will last anywhere from 40 minutes (with a 50Ah battery) to 2.7 hours (with a 200Ah battery) when powering a 400W inverter.
  • A 12V lithium (LiFePO4) battery will last anywhere from 1.3 hours (with a 50Ah battery) to 5.4 hours (with a 200Ah battery) when powering a 400W inverter.
How long will a battery run a 400-watt inverter?

12v 100Ah battery will run a 400W inverter for 2.6 hours which will fully discharge the battery from 0-100% so which 100Ah lead-acid or AGM battery with 50% DOD limit it will run for 75 minutes

How many batteries do I need for a 400-watt inverter?

you'll need 2 x 12v 100Ah lithium batteries in order to run your 400w inverter for 5 hours or 4 x 12v 100ah lead-acid or AGM batteries

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I hope this guide was helpful to you, if you have any queries contact us or LEAVE A COMMENT. Thanks!

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Chris Tsitouris is a renewable energy professional with 10+ years of experience as Director of Engineering at Solar Spectrum, previously working as Project Manager at SunPower and Energy Analyst at the National Renewable Energy Laboratory. As a thought leader, Chris has authored numerous articles and research papers.

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