Calculate exactly how long a battery will last based on capacity (Ah) and current draw (Amps). Features advanced settings for Peukert's Law, C-Ratings, and Depth of Discharge (DoD) for accurate engineering estimates.
This battery life calculator was inspired by a real engineering problem: estimating how long a battery system could reliably support critical equipment when failure was not an option. During electrical maintenance planning, simple battery math often looked acceptable on paper—but real-world systems are rarely that forgiving. Load variations, battery chemistry, discharge rate, and safety margins can dramatically affect actual runtime. That gap between theoretical estimates and operational reality is exactly why this tool was built.
Many online battery calculators use overly simplified formulas, often assuming battery capacity behaves the same under all conditions. In practice, battery performance changes based on current draw, chemistry, temperature, and discharge characteristics. Whether you are sizing a UPS backup system, planning a solar battery bank, designing an off-grid setup, or simply estimating runtime for electronics, understanding these variables can help prevent underperformance, downtime, or poor planning.
Our goal was to create a more practical battery runtime calculator that goes beyond basic amp-hour division. By considering factors like battery type, discharge behavior, and safety assumptions, users can get a more realistic estimate for both professional and everyday scenarios. For engineers, technicians, and DIY users alike, better calculations can support smarter equipment selection and safer system expectations.
Important Practical Note: Battery calculations should always be treated as estimates, not guarantees. Real-world battery life can be affected by temperature, battery age, inverter efficiency, depth of discharge, cable losses, and manufacturer-specific characteristics. For critical systems, conservative planning and datasheet verification remain essential. In both industrial and consumer settings, the safest battery plan is usually the one that assumes real conditions—not ideal ones.
The basic formula is Time = Capacity (Ah) / Current (A). However, this calculator uses a modified Peukert's Law formula to account for efficiency losses at high discharge rates, providing a much more realistic estimate than simple division.
DoD indicates the percentage of the battery that has been discharged. Using 100% of a battery's capacity often damages it. To extend battery life, we recommend setting the DoD slider to 50% for Lead Acid batteries and 80% for Lithium-ion (Li-ion) or LiFePO4 batteries.
Batteries become less efficient as you draw power faster. This is known as the Peukert Effect. Internal resistance generates heat, wasting energy that would otherwise power your device. Our calculator adjusts for this "shrinkage" of capacity automatically.
The C Rating specified on a battery is defined by the rate of time it takes to safely charge or discharge a battery. A 1C rating means the battery will empty in 1 hour. A 10C rating means it can empty in 6 minutes (1/10th of an hour). Knowing the C-rating ensures you don't draw more current than the battery can safely handle.