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.
Also, I’ll share some other factors which can affect the battery runtime
Battery Runtime Calculator
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!)
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 Capacity||Battery Type||Est. Runtime|
|50ah||Lithium (LiFePO4)||1.3 hours|
|60ah||Lithium (LiFePO4)||1.6 hours|
|70ah||Lithium (LiFePO4)||1.9 hours|
|100ah||Lithium (LiFePO4)||2.7 hours|
|150ah||Lithium (LiFePO4)||4 hours|
- 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
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
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
- How Long Will A 12v Battery Last With 500w Inverter?
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