UPS Runtime for Hub Calculator

1) Bank energy (Wh)
BankWh = (BatteryV × Series) × (CapacityAh × Parallel)

2) Usable energy (Wh)
UsableWh = BankWh × (1−Reserve) × (1−Aging) × Discharge × TempFactor × Efficiency × PeukertFactor

3) Runtime (hours)
RuntimeHours = UsableWh ÷ TotalLoadW

Load profile for connected garden systems

A hub, router, and sensor bridge usually draw steady power all day. Many hubs sit between 6–15 W, routers 5–12 W, and small repeaters 1–3 W each. Small loads look harmless, but they drain batteries over long outages. Measure watts with a plug-in meter, then include cameras, modems, or PoE injectors if installed.

Battery bank configuration and labels

Series connections raise voltage while parallel connections raise amp-hours. Both affect total watt-hours: Wh = V × Ah. Capacity is commonly rated at a 20-hour rate, so faster discharge reduces usable energy. Match the “Ah rating hour rate” to your label, and enter the correct series and parallel counts to reflect your wiring.

Derating for reserve, aging, and weather

Runtime drops when you hold reserve capacity, account for aging, or limit depth of discharge. A 15–25% reserve helps cover startup surges and low-voltage cutoffs. Aging derate reflects reduced capacity from cycles and storage. Cold weather can cut effective capacity noticeably in sheds; warmer conditions can shorten service life. The temperature factor converts ambient conditions into a practical estimate.

Efficiency and discharge behavior

Inverter and UPS stages waste energy as heat. Compact standby units often deliver 80–90% efficiency, while lightly loaded systems can vary. Enter a realistic efficiency value rather than a best-case brochure number. The Peukert setting models capacity loss under higher current draw; higher exponents reduce runtime more aggressively.

Using results to plan upgrades

Compare your target runtime with storm history, irrigation schedules, and remote access needs. If you need six hours but the estimate shows three, add parallel batteries, reduce the load, or improve efficiency. Keep the same reserve and derating assumptions when comparing options. Export CSV or PDF to document your baseline and validate improvements after hardware changes. For critical alerts, set a minimum runtime threshold and recheck after adding devices. A small watt increase can erase hours of backup. Re-run the calculator seasonally, because temperature and battery aging shift results over time.

1) How do I estimate hub wattage if I cannot measure it?

Use the device label for input power, then add the router and any bridges. If only volts and amps are listed, multiply them to get watts. Add 10–20% for adapters and conversion losses.

2) What reserve percentage should I choose?

For reliable operation, many users pick 15–25%. Reserve covers surge events, battery cutoffs, and measurement error. If your UPS shuts down early under load, increase reserve and retest.

3) Why does cold temperature reduce runtime so much?

Battery chemistry delivers less usable capacity when cold, and voltage sag reaches cutoff sooner. If your batteries sit outdoors or in a shed, use your typical night temperature for a more realistic runtime estimate.

4) When should I adjust the Peukert exponent?

If you use lead-acid batteries and the load current is high relative to capacity, Peukert losses increase. Use 1.05–1.15 for many lead-acid types. For lithium packs, a lower value is often appropriate.

5) How can I extend runtime without buying more batteries?

Reduce the load: disable nonessential cameras, lower Wi‑Fi transmit power if possible, or power a modem only when needed. Improve efficiency by using DC power where supported and avoiding unnecessary inverter stages.

6) Why does adding one small device change hours of runtime?

Runtime is usable energy divided by total watts. When the load is small, each extra watt is a big percentage increase. That percentage cuts runtime directly, so small additions can remove large chunks of backup time.