Calculate your battery capacity
Calculate how long your battery will last and find the perfect battery size for your needs Accurate calculations with our battery capacity calculator
Battery Parameters
Battery Runtime Results
Runtime Hours
Watt-Hours
Usable Capacity
Load Current
Battery Capacity Comparison
| Battery Type | Typical Capacity | Depth of Discharge | Energy Density | Common Applications |
|---|---|---|---|---|
| LiFePO4 | 20-300Ah | 80-100% | 90-120 Wh/kg | Solar, EVs, Marine |
| Lithium-ion | 2-100Ah | 80-90% | 100-265 Wh/kg | Electronics, Power tools |
| AGM | 20-200Ah | 50-80% | 30-50 Wh/kg | UPS, RVs, Marine |
| Flooded Lead Acid | 30-250Ah | 50-70% | 30-40 Wh/kg | Automotive, Backup |
Understanding Battery Capacity Calculations
Our battery capacity calculator helps you estimate how long your battery will last based on your specific power usage. By considering variables like battery voltage, discharge rate, chemistry, and inverter losses, the tool delivers reliable, real-world performance predictions.
Key Calculation Factors
Battery chemistry plays a major role in capacity and efficiency. AGM batteries and lithium iron phosphate (LiFePO4) batteries have different discharge profiles, which directly impact runtime and battery performance across solar and backup systems.
System voltage affects how efficiently energy is delivered. Higher voltage setups reduce current draw, minimizing energy loss and improving overall performance.
Practical Applications
Using a battery capacity calculator is essential when sizing your battery bank for an off-grid or solar setup. It ensures your system can meet daily energy needs without overloading or underutilizing the batteries.
It also helps you estimate how long your backup power will last during grid outages, keeping essential appliances and systems running when needed most.
Battery Capacity Fundamentals
Understanding battery capacity is essential for designing reliable power systems:
- Amp Hours (Ah): Capacity measurement indicating how much current a battery can supply over time (e.g., 100Ah = 5A for 20 hours)
- Watt Hours (Wh): Total energy capacity (Voltage × Amp Hours)
- Depth of Discharge (DoD): Percentage of battery capacity that can be safely used
- C-Rate: Charge/discharge rate relative to capacity (1C = full capacity in 1 hour)
Understanding battery capacity calculator is essential for designing efficient solar and backup power systems. Measured in amp-hours (Ah), battery capacity determines how much energy can be stored and delivered over time.
Calculating Battery Runtime
To calculate battery runtime accurately, begin by checking the amp-hour (Ah) rating of your battery. This value tells you how much energy the battery can store.
Next, identify the system voltage ypically 12V for solar and backup setups. Multiply the Ah rating by the voltage to get the total watt-hours (Wh) your battery can deliver.
Apply the Depth of Discharge (DoD) percentage. For example, if using 80% DoD, multiply the total watt-hours by 0.80 to get usable energy capacity.
Finally, divide the result by your device or load wattage. This gives you the runtime in hours. You can also use a battery runtime calculator to simplify this process and improve accuracy.
Example Calculation:
100Ah 12V battery with 300W load at 80% DoD and 90% inverter efficiency:
Usable Wh = 100Ah × 12V × 0.80 = 960Wh
Runtime = 960Wh ÷ (300W ÷ 0.90) = 960 ÷ 333.33 ≈ 2.88 hours
Battery Selection Guide
Choose the right battery type for your application:
LiFePO4
Best for: Solar systems, EVs, marine
Pros: Long lifespan, deep discharges, safe
Cons: Higher upfront cost
Lithium-ion
Best for: Electronics, power tools
Pros: High energy density, lightweight
Cons: Sensitive to overcharging
AGM/Lead Acid
Best for: Automotive, backup power
Pros: Affordable, reliable
Cons: Shorter lifespan, heavier
Tip: For solar systems size your battery bank to cover 2–3 days of autonomy with 50–80% daily DoD.
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.