A 12v 200ah battery will run an appliance that requires 400W for between 2.7 hours (with lead-acid battery type, 50% DoD limit) to 5.4 hours (with lithium battery type, 100% DoD limit)
Keep reading I’ll explain how you can calculate how long will your 200ah battery run on a 400-watt appliance and also some shortcomings of all these methods
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%.
After entering the information, click “Calculate” button to find out how long the battery last running a load.
Video – All about battery basics (Must watch!)
Steps to calculate 200ah battery runtime on 400-watt appliance
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 200ah battery
200ah battery in watts = 200 * 12 = 2400 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 = 2400 * 50% = 1200wh
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 = 1200 * 90% = 1080 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 200ah battery
200ah battery runtime on 400w appliance = 1080 / 400 = 2.7 hours
How long will a 200Ah battery run an appliance that requires 400W
here’s a chart on how long will a 12v, 24, and 48v 200ah lead-acid or Lithium battery will last on 400-watt load.
|Battery Capacity||Battery Type||200ah Battery Runtime on 400w|
|12v 200ah||Lead-acid||2.7 hours|
|24v 200ah||Lead-acid||5.4 hours|
|48v 200ah||Lead-acid||11 hours|
|12v 200ah||Lithium (LiFePO4)||5.4 hours|
|24v 200ah||Lithium (LiFePO4)||11 hours|
|48v 200ah||Lithium (LiFePO4)||22 hours|
Assumptions & Shortcomings of All These Methods
Here are some extra yet important points to keep in mind when figuring out how long your 200ah battery will last running a 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 )
200ah lead-acid Batteries are rated for 10 amps over 20 hours of time:
- Especially lead-acid type batteries are designed to be discharged at 20 hours. ( means 200ah lead-acid batteries are recommended to be discharged @ 10 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 200 amps then it’s will not last 30 minutes ( keep in mind the 50% DoD limit ). but it may last about 15-20 minutes.
- Check the battery discharge rate on the specs sheet of your battery or it’ll be mentioned on the battery (1h → 1C, 2h → 0.5C, 5h → 0.2C, etc.)