The most common question we get about battery backup for network gear is also the simplest to answer: how long will it actually run? Here is the math, with real numbers.
The runtime formula
Runtime (hours) ≈ battery watt-hours ÷ load watts × 0.9
The 0.9 accounts for DC conversion efficiency. That's all there is to it — the hard part is knowing your real load, which is usually much lower than the power adapter's rating.
Real-world examples with a 64Wh battery
A cellular router alone (5–7W) runs 8–11 hours. A router plus an ATA for phone lines (7–9W) runs 6–8 hours. Add a PoE camera or access point (15–20W total) and you get 3–4 hours. At the full 38W output of the ZP-64Wh, runtime is about 1.5 hours.
Why nameplate watts mislead
A router shipped with a 24W power adapter typically draws 5–8W in normal operation. Sizing backup from the adapter rating triples your battery cost for nothing. If you can, measure the actual draw — or start from typical figures: cellular routers 5–8W, ATAs 2–3W, IP cameras 4–12W, access points 6–15W.
Skip the double conversion
A traditional AC UPS loses 30–40% of its battery converting DC to 120V AC and back to DC. A DC mini UPS powers equipment directly at 9V, 12V, 24V or PoE, which is why a paperback-sized 64Wh unit outlasts a much larger AC UPS on the same load.
Want your own numbers? Use the runtime calculator, or see the ZP-64Wh Backup Power specs.
