What size UPS do I need for my NAS?

Rule of thumb: NAS watts × 1.6 × 1.3 = required VA. A 4-bay NAS at 50 W needs around 600-800 VA for 5-10 minutes of runtime. An 8-bay DIY at 110 W needs 1000-1500 VA.

Do I need pure sine wave for my NAS?

Synology explicitly recommends it. Modern NAS PSUs have Active PFC which can struggle with Modified Sine Wave. When in doubt: buy pure sine wave. The premium is $30-50.

Which UPS is Synology compatible?

Synology maintains an official compatibility list. APC Back-UPS Pro, CyberPower CP1500PFCLCD, Eaton Ellipse PRO are all on it. Verify before buying.

How long does a UPS battery last?

3-5 years. After that the capacity drops measurably. Models with replaceable batteries save money long-term: battery $30-60, vs. tossing the whole unit.

Is a cheap offline UPS under $70 enough?

Fine for a PC, marginal for NAS. 8-12 ms switch time may work, but Modified Sine Wave and no USB make a clean shutdown impossible. Don't cheap out here.

Best UPS for NAS 2026: What You Actually Need

Updated: 2026-04-29

A UPS isn't optional for a NAS, it's required. Power loss mid-RAID-write = data corruption or worst case a broken filesystem. Here's the 2026 picks with honest buying advice – no marketing bingo.

Short version

For a 4-bay NAS, an 800-1000 VA line-interactive UPS with pure sine wave is enough. 2026 picks: APC Back-UPS Pro 900, CyberPower CP1500PFCLCD, or Eaton Ellipse PRO 850. Must-haves: USB data link (NUT-compatible) and at least 5 minutes runtime at full load.

Why a UPS is mandatory for NAS

Three scenarios it protects against:

1. Corruption from unclean shutdown. RAID writes consist of multiple atomic operations. Power loss mid-write = inconsistent parity, worst case a lost file or a degraded ZFS pool.

2. Drive damage from voltage swings. Brownouts and spikes cause read/write errors and shorten drive life.

3. Brutal wear from reset loops. A brownout reset every few minutes during a thunderstorm night costs more drive life than 6 months of normal operation.

Calculate VA need correctly

Rule of thumb: NAS watts × 1.6 × 1.3 safety factor = required VA

Concrete examples:

2-bay Synology DS224+ + switch (~30 W): 30 × 1.6 × 1.3 = 62 VA → 350 VA UPS suffices
4-bay DS923+ + 4×16 TB drives (~50 W): 50 × 1.6 × 1.3 = 104 VA → 600-800 VA UPS
8-bay DIY with Ryzen 5 + 8×18 TB (~110 W): 110 × 1.6 × 1.3 = 230 VA → 1000-1500 VA UPS

More VA = longer runtime. Rule: 5-10 min covers a clean shutdown, 20-30 min is luxury.

UPS topologies that actually matter

Offline / Standby. Cheapest. Switches over only when power dies – ~10 ms gap. Fine for a PC, marginal for NAS. Not recommended.

Line-Interactive. Actively regulates voltage swings (AVR), ~3-5 ms switch time. Sweet spot for NAS. Every model recommended here is line-interactive.

Online / Double-Conversion. Power passes through the inverter permanently → no switch. 0 ms. Pricey ($300-800), for server racks. Overkill for home.

Pure sine wave vs Modified Sine Wave

Modified Sine Wave (stepped approximation) often works with Active PFC PSUs – but not always. Synology explicitly recommends pure sine wave. Modern NAS PSUs have Active PFC. When in doubt: buy pure sine wave. The premium is usually $30-50.

NUT and Synology compatibility

For your NAS to shut down cleanly during a power outage, it needs to communicate with the UPS – usually via USB.

Synology DSM has an official compatibility list. APC, Eaton, CyberPower and many others are on it.

TrueNAS, Unraid, OpenMediaVault use Network UPS Tools (NUT). The NUT HCL lists tested models.

Verify your model on the relevant list before buying.

Top 5 UPS picks 2026 for NAS

APC Back-UPS Pro BR900MI / 1500MI. Solid standard. Pure sine wave, 4 battery-backed outlets, USB. 900 VA / 540 W. Perfect for 2-4 bay NAS. ~$180.

CyberPower CP1500PFCLCD. 1500 VA, pure sine wave, well equipped, replaceable battery. ~$250.

Eaton Ellipse PRO 850. Premium build quality, very quiet, 850 VA / 510 W. ~$200.

APC Smart-UPS SMC1500I. One tier up. Optional network management card, 1500 VA. For homelabs or multiple devices. ~$430.

Eaton 5P 850i. Rack-mount 1U for homelab racks. 850 VA, NUT-compatible. ~$320.

What not to buy

Generic offline UPS under $70 – usually Modified Sine Wave, short battery life (1-2 years), no USB.

UPS without replaceable battery. After 3-4 years the battery dies and you toss the whole unit.

Non-sine-wave UPS for Synology/QNAP. Vendors explicitly exclude warranty for MSW operation.

Setup checklist

After purchase:

Plug UPS into wall, charge fully for at least 8 hours
USB cable to NAS
Enable UPS service on NAS (DSM: Control Panel → Hardware → UPS mode)
Set shutdown trigger: usually "30 seconds before battery empty" or "5 minutes on battery"
Test: with NAS running, pull the UPS plug, verify NAS shuts down cleanly

Recommendation

For 90% of home NAS: APC Back-UPS Pro 900 or CyberPower CP1500PFCLCD. Pure sine wave, USB, Synology-certified, replaceable battery. 5+ years of use with the occasional battery swap.

NAS Power Consumption 2026

NAS Buying Guide 2026

What happens when RAID fails?

RAID is not a backup