How Long Will A 12v Battery Run 400-watt Inverter? + Calculator

Need an easy solution? Enter the battery specs and the load connected with the inverter into our battery runtime calculator (given below) to find out how long will a 12v battery run a 400-watt inverter.

Easy! right?

Also, I’ll share some other factors which can affect the battery runtime

Battery Runtime Calculator

Battery Capacity
Battery Volts
Select Battery Type
Load Connected with inverter?
Total Load (watts)

Note! use my solar panel size calculator to find out what size solar panel you need to recharge your battery in desired hours with solar panels.


  • Inverter Efficiency: 90%
  • Lead-acid battery: 50% depth of discharge limit
  • Lithium (LiFePO4): 100% depth of discharge limit

Battery Depth of discharge DoD: is the percentage of the battery that has been discharged relative to the total battery capacity. The recommended depth of discharge limit for lead-acid, AGM, and gel batteries is about 50%. Only lithium (LiFePO4) batteries can be fully discharged to 100%.

How To Use The Calculator

  • Enter the battery capacity in amp-hours (Ah): Enter the battery capacity in amp-hours. for 100ah enter 100.
  • Enter the battery voltage: in this it’ll be 12v
  • Select the battery type:  Select “Lead-acid” if you’re using a flooded or sealed (AGM or gel) lead acid battery. Select “Lithium (LiFePO4)” if you use a lithium-iron phosphate battery.
  • load Connected with inverter?: in this scenario, select yes.
  • Enter total load in watts: if you’re running your 400-watt inverter at its full capacity then enter 400 otherwise if the output load is below 400 watts enter the value accordingly.

After entering the information, click “Calculate” button to find out how long will a 12v battery run a 400 watt inverter

Important! it’s not recommended to run your inverter at its full capacity always leave 20% of the capacity.

Example 1: how long will a car battery run a 400-watt inverter

A car battery will run a 400-watt inverter for about 50 minutes

Video – All about battery basics (Must watch!)

Watch this video to understand the basics of batteries: Their capacity, charge, and discharge rate.

Steps to calculate 12v battery runtime on 400 watt inverter

Follow these steps to calculate the battery life/runtime while running a load.


1- Converter battery ah into watt-hours (Wh). to calculate the battery capacity in watt-hours use this formula

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

let’s say you have a 12v 50ah battery

50ah battery in watts = 50 * 12 = 600 watt-hours 

2- Multiply the battery watt-hours by the battery depth of discharge limit. ( Default battery depth of discharge limit, Lead-acid battery: 50% DoD limit; Lithium: 100% DoD limit ). Let’s say you have a lead-acid type battery

Battery capacity in wh after DoD limit = 600 * 50% = 300wh

3- Multiply the battery capacity after the DoD limit with the inverter efficiency rate to calculate the AC watt-hours ( Most of the inverters are about 90% efficient)

Battery AC watts = 300 * 90% = 270 AC watt-hours 

4- Divide the battery AC watt-hours by the total load connected. Let’s say 400-watt appliance is connected to your 50ah battery

50ah battery runtime on 500w appliance = 270 / 400 = 0.6 hours or 40 minutes (hours to minutes = 0.6 * 60)

Note: There are some shortcomings of these methods which i’ll discuss at the end

How long will a 12v battery last with a 400-watt inverter?

here’s a chart on how long your 400W inverter will last on a 12v battery

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


  • 12v lead-acid battery will last anywhere from 40 minutes (on 50ah battery) to 2.7 hours (on 200ah battery)
  • 12v Lithium (LiFePO4) battery will last anywhere from 1.3 hours (on 50ah battery) to 5.4 hours (on 200ah battery)

Assumptions & Shortcomings of All These Methods

Here are some extra yet important points to keep in mind when figuring out how long will your 12v battery will last running a 400 watt inverter load

Battery life cycle count:

  • The storage capacity of the battery will decrease with every cycle ( a cycle is when you charge and discharge the battery to its DoD limit ).
  • if you have used your battery for a few hundred cycles then the result will be different. ( this factor isn’t included in my above-given methods )

Batteries are rated for 5 amps over 20 hours of time:

  • Especially lead-acid type batteries are designed to be discharged at 20 hours. ( means 100ah lead-acid batteries are recommended to be discharged @ 5 amps in order to maintain the battery health and reduce the discharge efficiency ).
  • on the other hand, AGM and lithium (LiFePO4) can be discharged at 50% of their capacity.
  • Discharging your battery at a higher rate will increase heat in the battery’s internal cells which will cause power loss. (this factor isn’t included in my above-given methods).
  • For example, if you discharge your lead-acid battery with 100 amps then it’s will not last 30 minutes ( keep in mind the 50% DoD limit ). but it may last about 10-15 minutes.
  • Check the battery discharge rate on the specs sheet of your battery or it’ll be mentioned on the battery
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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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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