A 12v 100ah lead-acid battery with a 50% DoD limit will run an appliance that requires 20W for about 27 hours
Keep reading I’ll explain how you can calculate how long will your 100ah battery run on a 20-watt appliance
How long will 100ah battery last – 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): in this case, it’ll be 100
Enter the battery voltage: is this a 12, 24, or 48-volt battery?
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?: Are you using an inverter to run the load or is the load connected directly through the battery?
Enter total load in watts: Enter the total load in watts (e.g 20 for 20 watts of output load)
After entering the information, click “Calculate” button to find out how long the battery last running a load.
Video – Solar battery 101
Steps To Calculate 100ah Battery Runtime On 20-Watt Appliance
Follow these steps to calculate the 100ah battery life/runtime while running a 20w load.
1- Converter battery ah into watt-hours (Wh). to calculate the battery capacity in watt-hours use this formula
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 = 1200 * 50% = 600wh
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 = 600 * 90% = 540 AC watt-hours
4- Divide the battery AC watt-hours by the total load connected. Let’s say 20-watt appliance is connected to your 100ah battery