GUARDSOURCEHQ TOOL
UPS Runtime Calculator
Size a battery backup for your cameras and NVR — or check how long the one you have will last.
RESULT
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Enter your system and press Calculate.
The one thing most people get wrong
Your cameras only keep recording if the PoE switch (or the NVR’s PoE ports) AND the NVR are both on the UPS. Backing up the NVR alone does nothing — the cameras go dark. This calculator already includes every device that has to stay powered.
Continue planning
Assumptions: camera draw by IEEE 802.3 PoE class (af ≈ 6 W, at ≈ 12 W, bt ≈ 24 W); NVR includes one hard drive; usable battery energy derated to 85% for inverter loss. Estimates for planning — confirm against your device labels.
Accuracy & Assumptions
This calculator gives a planning estimate based on the load and battery details you enter. It assumes a healthy battery and typical inverter efficiency, and it approximates camera draw by PoE class (IEEE 802.3af/at/bt). Real-world runtime usually runs shorter than the figure shown, depending on:
- Battery age and health — a battery loses usable capacity as it ages, so an older UPS runs shorter than its rating.
- Actual draw vs. nameplate — cameras with infrared, heaters, or pan-tilt-zoom motors pull more than their idle rating, especially at night.
- Inverter and conversion losses — a UPS never delivers 100% of its stored energy, so expect real runtime below the ideal figure.
- Temperature — cold or hot conditions reduce battery capacity and shorten runtime.
- Cutoff threshold — a UPS shuts down before the battery is fully drained to protect it, so usable runtime is less than the raw capacity implies.
Use the result to size a backup with headroom, not as a guaranteed runtime. If your system must stay online through a longer outage, choose a larger UPS or add a second battery.