Battery Runtime Calculator

This battery runtime calculator helps contractors, agricultural operators, and off-grid professionals estimate how long a battery or portable power station can run real equipment. Enter your loads, wattage, daily hours of use, autonomy target, and system efficiency to estimate runtime and the watt-hour capacity you may need before buying a portable power station, battery bank, or off-grid power setup.

Step 1
Daily Load Profile
Enter every load, its running wattage, and daily hours of use. Run all loads simultaneously? Add them all. Sequential? Add each with realistic hours.
Load / Device
Watts (W)
Hrs/Day
Wh/Day
Total Daily Load 0 Wh / day
Step 2
Autonomy + Efficiency
Set how many days the bank must run without recharging, and configure system losses.
1 day
1 day (daily recharge) 3-4 days 7 days
80%
50% (conservative / extends cycle life) 80% (LFP standard) 100%
Daily load carried forward 0 Wh / day
Step 3
Battery Bank Size
Minimum and recommended gross capacity for your setup
Complete Steps 1 and 2 to see your result

Battery Runtime Calculator for Jobsite and Off-Grid Power

This battery runtime calculator helps estimate how much usable battery capacity you need before choosing a portable power station, battery bank, or off-grid power setup. Instead of relying only on manufacturer runtime claims, the calculator uses your actual loads, watts, hours of use, autonomy target, and system efficiency.

For jobsite crews, farm operators, mobile technicians, and off-grid users, battery sizing is not just about total watt-hours. You also need to consider how long each device runs, whether loads operate at the same time, and how much reserve capacity you want available when weather, charging access, or work schedules change.

How the Battery Runtime Calculator Works

Start by entering each load you expect to run during a normal workday. This can include LED site lights, tool chargers, fridges, pumps, laptops, communication gear, or other equipment. The calculator converts watts and hours into daily watt-hours, then adjusts the result based on your autonomy and efficiency settings.

Autonomy means how many days you want the system to operate without fully recharging. Efficiency accounts for real-world losses from inverters, charging, wiring, and battery conversion. Energy.gov notes that energy storage is never 100% efficient because some energy is lost during storage and retrieval, which is why efficiency should be included in serious battery sizing calculations.

Why Battery Capacity Matters

A battery that is too small may work during light use but fail during a full workday. A battery that is too large may cost more than needed, take longer to recharge, and be harder to move. The goal is to estimate a practical minimum capacity and then compare that number against the usable watt-hour capacity of the power station or battery bank you are considering.

After using this battery sizing calculator, you can compare the result with a jobsite power calculator or review portable power station options for the type of work you actually do. For best results, always check both watt-hour capacity and output wattage before buying.

For general battery background, the U.S. Department of Energy explains that batteries store and release electricity on demand, which is why capacity, output, and efficiency all matter when designing a real-world power setup.

This tool also works as a basic battery sizing calculator because it converts load, runtime, and efficiency into estimated watt-hour capacity.

For broader grid and energy storage context, the U.S. Department of Energy Office of Electricity focuses on electricity reliability, grid resilience, and energy storage performance. The same logic applies at jobsite scale: battery runtime is not just about total watt-hours, but also load demand, efficiency losses, reserve capacity, and how long your equipment needs to operate between recharge cycles.