Runtime depends on how much energy the batteries hold and how hard the load draws. Enter the battery and load below for an estimated backup time. Treat it as optimistic, since real batteries deliver less at high load and as they age.
How to estimate UPS runtime
Total energy is amp-hours x voltage x number of batteries. Multiply by efficiency and depth of discharge for usable watt-hours, then divide by the load in watts for runtime in hours. Because higher loads cut usable capacity, add margin for aging batteries, cold temperatures, and future load growth.
Runtime by load (216 Wh usable)
| Load | Approx runtime |
|---|---|
| 150 W | ~78 min |
| 300 W | ~39 min |
| 600 W | ~19 min |
| 1000 W | ~12 min |
Frequently asked questions
How do I calculate UPS runtime?
Amp-hours x voltage x batteries for watt-hours, times efficiency for usable energy, divided by load in watts for hours. Times 60 for minutes.
Why is real runtime shorter?
Batteries deliver less at higher discharge rates (Peukert's law) and fade with age. Treat the figure as optimistic and add margin.
How much runtime do I need?
A few minutes for graceful shutdown; 10 to 30 minutes to ride through short outages or hand off to a generator. Always-on loads need more batteries.
Does a bigger load reduce runtime?
Yes, roughly in proportion. Doubling the load roughly halves runtime; adding batteries extends it by the same proportion.
What efficiency should I use?
Around 0.85 to 0.95; 0.9 is a reasonable default. Lower efficiency and depth of discharge give a safer estimate.
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