UPS Runtime Estimator for NAS: How Long Will Your NAS Stay On?
This UPS runtime estimator for NAS calculates how long your uninterruptible power supply will keep your NAS running during a power outage based on UPS capacity, NAS wattage, and battery age. Helps you decide if your current UPS provides adequate protection.
Estimate how long your UPS will keep your NAS running during a power outage, and whether that's enough time for a safe shutdown.
Power outages don't damage a NAS directly, but an unclean shutdown can corrupt files, break RAID arrays, and interrupt backup jobs. A UPS gives your NAS time to shut down gracefully, but only if the battery has enough capacity for your load.
Not sure how many watts your NAS draws? Use our NAS Power Cost Calculator to estimate consumption, then come back with the number.
Your Setup
Watts are conservative (slightly above typical published draw) since this feeds a safety estimate.
That's high for a NAS, make sure you're entering NAS consumption only, not the whole rack.
W
W
W
30 WNAS only
Wh = V × Ah. Check the battery label or search "[your UPS model] battery Wh".
Most modern Synology and QNAP units shut down in 1-2 minutes. If unsure, choose 2 minutes.
Battery Wh values for preset UPS models are sourced from manufacturer specifications. The age factor accounts for lead-acid battery degradation over time (new = 100%, 1-2 yr = 90%, 3-4 yr = 75%, 5+ yr = 55%). The efficiency factor adjusts for inverter losses, which vary by load percentage. The safety margin is a conservative multiplier applied to the raw formula result: a simple Wh/efficiency model like this one consistently overstates real, manufacturer-measured runtime (we've seen 50-300%+ overestimates when checked against published discharge curves), because it can't capture non-linear battery discharge, inverter self-consumption, and voltage cutoff behaviour. The margin brings the estimate closer to what you'd actually get.
This is still an estimate, not a guarantee. Actual runtime depends heavily on your specific UPS model, battery condition, ambient temperature, input voltage stability, and firmware behaviour. For a safety-critical setup, check your UPS manufacturer's own published runtime chart at your load, and test with your actual hardware by timing how long the UPS holds your load during a planned power-off.
Frequently Asked Questions
VA (volt-amperes) is the apparent power, the maximum the UPS can deliver in theory. Watts is the real power your devices actually consume. The ratio between them is the power factor (typically 0.6-0.7 for consumer UPS units). A 1000VA UPS might only deliver 550-600 watts of real power. Always check the watt rating, not just VA, when sizing a UPS. Neither VA nor watts tells you battery capacity, that's in Wh (watt-hours), which is what determines runtime.
Most modern Synology and QNAP NAS units complete a clean shutdown in 1-2 minutes. This includes flushing write caches, closing open files, stopping services, and parking drive heads. Larger arrays with many active services or parity checks in progress may take 3-5 minutes. The risk of an unclean shutdown is file corruption, broken RAID arrays, and interrupted backup jobs, so configure auto-shutdown even if your UPS seems large enough.
Most consumer UPS units (APC, CyberPower) connect to a NAS via USB. Synology supports this natively in Control Panel → Hardware & Power → UPS. QNAP has similar built-in support under Control Panel → System → UPS. Configure the NAS to shut down automatically when battery reaches a threshold (e.g., 30%) or after a set time on battery. Synology also supports "network UPS" mode where one device acts as the UPS server for others on the same network.
Lead-acid UPS batteries typically last 3-5 years depending on usage, temperature, and discharge frequency. Signs of a failing battery: the UPS beeps or shows a "replace battery" indicator, runtime drops noticeably, or the UPS fails to hold load during an outage. Replacement batteries for consumer UPS units cost $30-80 AU and are a straightforward swap on most models. Test annually by unplugging the UPS from the wall and timing how long it holds your load.
Yes, if you want your NAS to remain reachable during an outage. A modem and router together draw about 15-20 W, a modest impact on runtime, but it keeps your network alive. This means you can receive NAS shutdown alerts, access your NAS remotely to check status, and allow cloud backup services to complete or pause gracefully. Use the "Modem / Router" checkbox above to see the impact on your runtime.
For a typical 2-4 bay home NAS (25-40 W), a 600VA / 330W UPS gives roughly 35-55 minutes of conservatively-estimated runtime on a charged battery, more than the 1-3 minutes needed for a clean shutdown. If you're also powering a router and switch, step up to 750VA-1000VA for comfortable headroom. The goal isn't to run for hours, it's to give the NAS enough time to shut down cleanly and ride through brief outages (which are most outages). Treat any runtime figure as conservative, not a guarantee, and check your UPS manufacturer's own runtime chart for critical setups. Use this estimator to check your specific setup before buying.
Not normally. A UPS provides clean, conditioned power to your devices, and the opposite scenario is the real risk: without a UPS, power events like brownouts, surges, and sudden outages can corrupt NAS data, damage drives, and interrupt RAID rebuilds. Line-interactive UPS units also provide voltage regulation during brownouts, adding another layer of protection beyond just battery backup. One caveat: a simulated/stepped sine wave UPS can be incompatible with some active-PFC power supplies, check your NAS spec sheet, and choose pure sine wave if in doubt (see the AU note below).
For home NAS use, line-interactive is the sweet spot. It corrects minor voltage fluctuations without switching to battery (extending battery life) and switches to battery in 2-5 ms, fast enough that a NAS power supply won't notice. Standby UPS units are cheaper but switch slower (5-12 ms) and don't regulate voltage. Online (double-conversion) UPS units provide the cleanest power with zero transfer time, but they're expensive, less efficient, and generate more heat, overkill for a home NAS. Most APC BX and CyberPower VP models sold in Australia are line-interactive.
AU UPS Pricing Reference: NAS Protection (early 2026)
UPS units suitable for NAS protection in Australia. AU power standard: 230V nominal (AS 60038), 50Hz. Prices from Mwave, PLE, Amazon AU.
UPS
Capacity
AU retail (approx)
Best for
APC BX950MI
950VA / 520W
$160-$200
2-bay NAS + switch: ~35 min conservatively-estimated runtime at 60W load
APC BX1600MI
1600VA / 900W
$280-$340
4-bay NAS + router + switch: 50-65 min at 80W load (manufacturer curve)
CyberPower CP1500EPFCLCD
1500VA / 900W
$420-$470
Pure sine wave, recommended for NAS with sensitive PSUs
APC SMT1000I
1000VA / 700W
$1,000-$1,100
Smart UPS: USB management, Synology/QNAP UPS integration
Eaton 5E 1200
1200VA / 660W
$180-$230
Budget option, adequate for single NAS + switch
AU Power Outage Context
Australian power outages are typically brief, most outages last under 30 minutes. A UPS for NAS does not need to power the NAS indefinitely; it needs to provide enough runtime to either:
Ride out short outages (most AU residential outages): 10-20 minutes coverage is usually sufficient
Trigger a clean shutdown via USB or network UPS communication, most Synology and QNAP units support APC and CyberPower USB integration natively
Australian networks report roughly 65-115 minutes of total outage time per customer per year on average (AER network performance/SAIDI data, varies by network and region), spread across the year rather than one long event. A 950VA UPS provides adequate protection for most AU home NAS users.
AU pure sine wave note: Most AU NAS units with switching power supplies work with simulated sine wave (AVR) UPS output. However, for NAS units with active PFC power supplies (check your NAS spec sheet), a pure sine wave UPS is required, simulated sine wave can cause shutdown or PSU damage. When in doubt, choose pure sine wave (e.g., CyberPower CP1500EPFCLCD or APC SMT series).