Question 1

What's the difference between a line-interactive and an online double-conversion UPS?

Accepted Answer

A line-interactive UPS uses AVR to correct voltage fluctuations and only switches to battery during a full power failure, with a transfer time under 4ms. An online double-conversion UPS runs all connected equipment through its inverter continuously, meaning zero transfer time and completely clean power output — but at the cost of lower efficiency (85–90%) and higher heat output. For most office and SMB use, line-interactive is the better practical choice. Online double-conversion is worth the premium only for servers or equipment that genuinely cannot tolerate any power interruption.

Question 2

How do I calculate what VA rating I need?

Accepted Answer

Add up the wattage of everything you plan to connect, then divide by 0.8 to give yourself a 20% headroom buffer — that's your minimum VA requirement. Most desktop PCs draw 200–400W under load; a 1U server might pull 300–500W; a network switch typically 50–150W. A 1000VA unit (rated around 700W) comfortably handles a mid-range server plus a monitor and a switch. If in doubt, size up — running a UPS at 60–70% capacity rather than 80% extends both battery life and runtime.

Question 3

How long will a UPS actually run during a power cut?

Accepted Answer

Expect 5–10 minutes at full load for most standard units — enough time for an automatic graceful shutdown, which is the real goal. Manufacturer runtime figures are typically quoted at 50% load, so halve them for a realistic estimate under heavy use. If you need 30 minutes or more, look for models that support external battery modules (EBM), such as the APC Back-UPS Pro range. Runtime drops sharply as load increases, so the single most effective way to extend it is to reduce what's connected.

Question 4

Is a cheap offline UPS worth buying, or should I avoid them?

Accepted Answer

For basic desktop protection, an offline UPS is perfectly adequate — but know what you're getting. The 4–6ms transfer time is fine for a home PC or router, but it can cause sensitive equipment, older servers, or some NAS devices to reboot rather than ride through the outage. The bigger risk is buying a no-name offline unit with a poor battery and no management software. Stick to known brands (APC Back-UPS, Eaton 3S) even at the budget end — the battery quality and replacement availability alone justify the modest price difference.

Question 5

Do I need a UPS with a Network Management Card (NMC)?

Accepted Answer

Only if you're managing multiple UPS units remotely or integrating with a monitoring platform like Nagios, PRTG, or Zabbix. For a single UPS protecting one server, USB with PowerChute or Intelligent Power Manager software is entirely sufficient. NMC becomes essential when you have several units across a network, need SNMP traps for alerting, or require centralised firmware updates. The APC SMT1500RMI2UNC ships with an NMC pre-installed — a genuine convenience, though you pay a significant premium for it.

Question 6

How often should I replace the battery in my UPS?

Accepted Answer

Every 3–5 years under normal conditions, or sooner if the unit starts alarming or runtime drops noticeably. Heat is the main enemy of UPS batteries — a unit running in a warm server room will degrade faster than one in a climate-controlled environment. Most modern UPS units run a self-test cycle (often weekly) and will flag a failing battery via their management software. Don't ignore these warnings: a UPS with a degraded battery offers almost no protection and may fail silently during an actual outage.

Question 7

What's the best UPS brand for a small business server room in 2026?

Accepted Answer

APC and Eaton are the two safest choices for SMB server room deployments, and the decision often comes down to budget and ecosystem. APC's Smart-UPS range has the widest replacement battery availability in the UK and the most mature SmartConnect cloud monitoring platform. Eaton's 5SC and 5PX lines offer comparable protection at a lower average price point, with excellent Intelligent Power Manager software. PowerWalker is worth serious consideration for double-conversion requirements on a tighter budget — their VFI IoT range delivers genuine online UPS performance at prices that undercut APC and Eaton meaningfully.

Uninterruptible Power Supplies (UPSs) Price Comparison

APC Smart-UPS SMT3000RMI2UC- 8x C13, 1x C19, USB, Rackmount 2U, SmartConnect, 3000VA

APC Smart-UPS On-Line, 1500VA/1500W, Rackmount 2U, 230V, 6x C13 IEC outlets, SmartSlot, Extended runtime, W/ rail kit

APC Back-UPS, 650VA/400W Floor/Wall Mount, 230V, 8x British BS1363A outlets, USB Type A Port, User Replaceable Battery

APC Back-UPS BE850G2-UK - 8x BS 1363 outlets, 850VA, 2 USB chargers, 1 USB data port

APC BR650MI uninterruptible power supply (UPS) Line-Interactive 0.65 kVA 390 W 6 AC outlet(s)

APC Back-UPS PRO BR900MI - 6x C13 output, USB, 900VA

APC Back-UPS, 950VA, Tower, 230V, 6x IEC C13 outlets, AVR

APC Back-UPS, 2200VA, Tower, 230V, 6x IEC C13 outlets, AVR

APC Back-UPS, 1600VA, Tower, 230V, 6x IEC C13 outlets, AVR

APC Back-UPS, 1200VA, Tower, 230V, 6x IEC C13 outlets, AVR

Eaton 9PX3000IRTNBS uninterruptible power supply (UPS) Double-conversion (Online) 3 kVA 3000 W 10 AC outlet(s)

Uninterruptible Power Supplies (UPSs) Price Comparison