⚡ UPS Run Time Calculator
Calculate Runtime
Calculate Battery Capacity
Typical 80‑95%
Formula: Runtime (h) = (Ah × V × efficiency/100) / Load (W)
Runtime
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Battery energy
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Load
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Efficiency
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Key formulas
Battery energy (Wh) = Capacity (Ah) × Voltage (V)
Usable energy (Wh) = Wh × (Efficiency/100)
Runtime (h) = Usable energy / Load (W)
Required Ah = (Load × runtime) / (V × efficiency/100)
People Also Ask
⏱️ How long will a 7Ah 12V battery run a 100W load?
Energy = 7Ah × 12V = 84Wh. With 85% efficiency, usable = 71.4Wh. Runtime = 71.4Wh / 100W = 0.714h ≈ 43 minutes.
🔋 What efficiency should I use?
Typical inverter/ UPS efficiency is 80‑95%. For rough estimates, 85% is a good average. High‑quality units may reach 90‑95%.
📊 Does battery voltage affect runtime?
Yes, higher voltage means more watt‑hours for the same Ah rating. For example, 100Ah at 12V = 1200Wh, at 24V = 2400Wh.
⚡ Can I run a 500W device from a small UPS?
Check the UPS capacity (VA/W). A typical 7Ah UPS is rated ~300‑400W. Running 500W may overload it. Use our calculator to see if battery can supply enough energy.
Common UPS battery configurations
| Application | Typical Ah | Voltage | Approx runtime at 100W |
|---|---|---|---|
| Small desktop UPS | 7‑9 | 12V | 40‑60 min |
| Mid‑tower UPS | 12‑18 | 12V | 1‑2 h |
| Server UPS | 24‑40 | 24‑48V | 2‑4 h |
| External battery pack | 50‑100 | 12‑24V | 4‑10 h |
| Telecom backup | 100‑200 | 48V | 8‑20 h |
Runtime estimates assume 85% efficiency. Actual runtime may vary with load and battery age.
Frequently Asked Questions
How accurate is this calculator?
It provides a theoretical estimate. Actual runtime depends on battery health, discharge rate (Peukert effect), temperature, and exact inverter efficiency. Use as a guideline.
What is Peukert's law?
Battery capacity decreases at high discharge rates. For example, a 100Ah battery may deliver only 70Ah if discharged at 50A. Our calculator uses nominal capacity; for high loads, real runtime may be lower.
Can I use this for lithium batteries?
Yes, lithium batteries have higher usable capacity (often 90‑95%) and efficiency. The same formulas apply; adjust efficiency accordingly (typically 95%+).