Battery Capacity Calculator
Estimate how long your battery will last and find the ideal battery size for your solar, EV, or backup system. Accurate calculations made simple.
Battery Parameters
Battery Runtime Results
Runtime Hours
Watt-Hours
Usable Capacity
Load Current
Understanding Battery Capacity Calculations
Our calculator estimates how long your battery will last based on voltage, discharge rate, chemistry, and inverter losses. Perfect for solar, EV, and backup systems.
Key Calculation Factors
Battery chemistry, system voltage, and depth of discharge directly affect runtime and performance.
Practical Applications
Use this tool to size battery banks for off-grid setups or to estimate backup runtime during outages.
Battery Capacity FAQs
Battery capacity is calculated using Amp Hours (Ah) or Watt Hours (Wh). Multiply current (amps) by time (hours) for Ah, and multiply voltage by Ah for Wh.
Formula: Wh = Ah × V. Example: 100Ah × 12V = 1,200Wh.
A 150Ah 12V battery with 80% DoD and 90% inverter efficiency can run a 300W load for around 4.3 hours.
Use a battery runtime calculator for accurate results.
A 100Ah 12V battery at 80% DoD and 90% inverter efficiency will power a 200W load for about 4.3 hours.
For lithium batteries (100% DoD), runtime increases to roughly 5.4 hours.
100Ah means the battery can deliver 100 amps for 1 hour or 10 amps for 10 hours. It defines the storage capacity.
In a 12V system, 100Ah equals 1,200Wh of total energy.
Estimate daily energy usage (Wh), multiply by days of autonomy, and divide by DoD and system voltage to get Ah.
Use a solar battery calculator for fast sizing.
Series: Increases voltage, capacity stays same. Parallel: Voltage same, capacity increases. Combine both for higher power and runtime.
Cold reduces capacity and performance. Heat increases degradation. Ideal temperature is 20–25°C for optimal battery efficiency.
Use the formula: Wh = Ah × V. Lithium batteries often allow 95–100% DoD, so more usable energy compared to lead-acid.
For runtime, divide total usable Wh by load power in watts.