Battery Watt Calculator
Calculate battery energy in watt-hours (Wh), convert between Ah and Wh, and estimate runtime under any load with depth of discharge.
Calculate Battery Energy
Enter battery voltage, amp-hour rating, load, and depth of discharge to calculate stored energy and runtime.
How to Calculate Battery Watt-Hours
Battery energy in watt-hours (Wh) equals voltage (V) multiplied by amp-hour capacity (Ah): Wh = V × Ah. A 12V 100Ah battery stores 1,200 Wh (1.2 kWh) of energy.
Battery Chemistry Comparison
| Chemistry | Nominal Voltage | Max DoD | Cycle Life | Best For |
|---|---|---|---|---|
| Lead-Acid (FLA) | 12V | 50% | 300-500 | Budget backup |
| AGM | 12V | 50% | 400-800 | RV, marine |
| LiFePO4 | 12.8V | 80-100% | 2,000-5,000 | Solar, RV, off-grid |
| Li-ion (NMC) | 3.7V/cell | 80-90% | 500-1,500 | Laptops, EVs |
| Li-ion (Tesla PW) | ~50V | 100% | 3,000+ | Home battery |
Battery Runtime Examples
| Battery | Energy (Wh) | 100W Load | 300W Load | 500W Load |
|---|---|---|---|---|
| 12V 50Ah (Lead, 50% DoD) | 300 Wh usable | 3.0 hrs | 1.0 hr | 0.6 hrs |
| 12V 100Ah (Lead, 50%) | 600 Wh usable | 6.0 hrs | 2.0 hrs | 1.2 hrs |
| 12.8V 100Ah (LiFePO4, 80%) | 1,024 Wh usable | 10.2 hrs | 3.4 hrs | 2.0 hrs |
| 48V 100Ah (LiFePO4, 80%) | 3,840 Wh usable | 38.4 hrs | 12.8 hrs | 7.7 hrs |
Frequently Asked Questions About Battery Watt-Hours
How do I convert Ah to Wh?
Multiply amp-hours by voltage: Wh = Ah × V. A 12V 100Ah battery = 1,200 Wh. A 48V 50Ah battery = 2,400 Wh. Always use the nominal voltage of the battery chemistry.
What is depth of discharge (DoD)?
Depth of discharge is the percentage of total battery capacity that has been used. A 100Ah battery at 50% DoD has discharged 50Ah. Lead-acid batteries should not exceed 50% DoD for longevity. LiFePO4 batteries can safely discharge to 80-100% DoD.
How long will a 12V 100Ah battery last?
A 12V 100Ah battery stores 1,200 Wh. At 100W load with 50% DoD (lead-acid): 600 Wh ÷ 100W = 6 hours. With LiFePO4 at 80% DoD: 960 Wh ÷ 100W = 9.6 hours. Runtime depends on battery type, DoD, and load.
What is the difference between Wh and W?
Watts (W) measure instantaneous power — how fast energy is being used right now. Watt-hours (Wh) measure total energy — how much energy is stored or consumed over time. A 100W light running for 5 hours uses 500 Wh of energy.
Does temperature affect battery capacity?
Yes, cold temperatures significantly reduce battery capacity. Lead-acid batteries lose ~20% capacity at 32°F (0°C) and ~40% at 0°F (-18°C). LiFePO4 batteries lose ~10-20% at freezing. Always size batteries with a temperature margin for cold climates.