A CCTV UPS has to carry the NVR, the PoE switch and every camera the switch powers, not just the recorder. Sixteen cameras at 7 W, one PTZ, an NVR and a router come to about 217 W from the mains; buy a UPS rated at least 271 W (339 VA), and two 12 V 9 Ah batteries give roughly 22 minutes on this calculator's battery model. This calculator works out the load, the rating and the minutes for your own setup, and how many batteries a target backup time needs.
Last checked: 14 Oct 2026.
How the calculator works
Inputs: PoE cameras and PTZs with their peak draw, the NVR with its disks, switch electronics and router, the battery bank (number of 12 V batteries and Ah each) and the backup you want.
Load (W) = (cameras × W + PTZ × W) ÷ 0.85 + NVR + switch and router
UPS rating (W) = load × 1.25; VA = W ÷ 0.8
Watts each battery must give = load ÷ 0.85 ÷ batteries
Minutes = read from the battery's constant-power discharge table, derated 20%
Labelled assumptions in those formulas:
- 0.85 for the PoE switch's power supply and again for the UPS inverter: a planning efficiency, not a measured one.
- 25% headroom on the UPS rating, and 0.8 W per VA to convert. The 0.8 matches the Schneider Electric (APC) Easy UPS SRV 1000 VA (SRVS1KI), a double-conversion online unit rated 1,000 VA and 800 W (Schneider product datasheet dated 22 Apr 2021, hosted by Farnell, checked 14 Oct 2026). Small line-interactive UPS units are often rated lower in watts per VA; buy on the watt rating.
- 20% battery derating for ageing and temperature.
Why minutes are not just Ah × volts. A lead-acid battery gives less energy the faster you drain it. CSB's datasheet for its GP1272 F2 12 V battery lists 168 W for 15 minutes but 57.4 W for 60 minutes to 1.75 V per cell (datasheet RA260131, checked 14 Oct 2026). That is 42 Wh in a 15-minute drain against 57 Wh in an hour. The calculator interpolates in that table and scales it in proportion to your battery's Ah, taking the GP1272 F2 as 7.2 Ah. That 7.2 Ah is an assumption taken from distributor listings, such as one quoting "Rated capacity C20: 7.2 Ah (20hr)" (checked 14 Oct 2026); the CSB datasheet checked does not print an Ah figure. Linear scaling by Ah is also an assumption. Beyond 90 minutes the calculator extrapolates.
The same effect shows in UPS datasheets: the SRV 1000 VA lists 24 minutes at 200 W but 11 minutes at 400 W on its internal battery. Doubling the load more than halves the backup. Those are that UPS's own figures, not an output of this calculator.
Worked example: 8, 16 and 32 cameras
Each row has one PTZ budgeted at 25.5 W (an assumption; larger outdoor PTZs can draw more) and fixed cameras at 7 W each with IR on (an assumption; the PoE budget calculator explains the camera figures). NVR draw including disks is assumed at 20, 30 and 45 W; switch electronics and router at 25 W for 8 and 16 cameras and 40 W for 32. Minutes come from the calculator's battery model above; treat them as ±25%.
| Cameras | Load (W) | Smallest UPS (W / VA) | 2 × 12 V 9 Ah (min) | 4 × 12 V 9 Ah (min) | 4 × 12 V 26 Ah (min) |
|---|---|---|---|---|---|
| 8 + 1 PTZ | 141 | 177 W / 221 VA | 39 | 89 | ~258 |
| 16 + 1 PTZ | 217 | 271 W / 339 VA | 22 | 53 | ~168 |
| 32 + 1 PTZ | 379 | 474 W / 592 VA | 10 | 27 | ~96 |
Figures above 90 minutes are extrapolated. The battery counts assume the UPS accepts that bank: internal batteries are fixed, and adding external ones needs a long-backup model with the right bank voltage (24, 36, 48 V and so on). Round the calculator's battery count up to your UPS's bank.
What the table says for a plant with a diesel generator: almost any of these banks covers the seconds a DG set takes to catch and stabilise. Long backup matters only where there is no generator, or where the camera circuit is not on it.
What this number does not tell you
- Whether the UPS survives the generator. Changeover power from a DG is dirty; the PoE explainer explains why an online double-conversion UPS is the safer choice there.
- Whether the switch is on the UPS at all. A UPS on the NVR alone keeps the recorder running while every PoE camera is dark.
- Battery health. A three-year-old battery may give far less than the table. Test by switching off the mains at the board, during the day, and timing it.
- What happens to the disks after a hard cut. If the UPS runs out before the NVR shuts down, the disk can come back as uninitialized. See NVR HDD shows uninitialized after a power cut before formatting anything.
Related guides
- NVR HDD Shows Uninitialized, Abnormal or No Disk After a Power Cut
- PoE Power Budget for Factory Cameras in India: Sizing It Right
- PoE budget calculator
- CCTV upload bandwidth calculator
FAQ
What size UPS do I need for 16 CCTV cameras and an NVR? With 16 cameras at 7 W, one PTZ, an NVR and a router, the load is about 217 W. Buy a UPS rated at least 271 W, about 339 VA at 0.8 W per VA. Two 12 V 9 Ah batteries give roughly 22 minutes on this model.
How long will a UPS run my CCTV system? It depends on load and battery, and not linearly. One 1,000 VA online UPS datasheet (Schneider Easy UPS SRV) lists 24 minutes at 200 W and 11 minutes at 400 W on its internal battery. Enter your load and battery bank in the calculator for an estimate, then test it.
Should PoE switches be on the UPS? Yes. PoE cameras take their power from the switch, so if the switch loses power every camera goes dark, even while the NVR itself stays on.
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