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Summary
Three boxes on the shop shelf look almost identical and cost between $10 and $200: a power strip, a surge protector, and a battery backup. This article explains what each one actually protects, how to size a battery backup for a normal desk, and which device you must never plug into one.
Before You Start
None required. This is background reading before you buy, or a sanity check on what is already under your desk.
Instructions
1. Power Strips Protect Nothing
This is the part that surprises people. A plain power strip is an extension lead with six sockets. It contains a cable, a switch, sometimes a fuse, and nothing else. It does not stop a voltage spike reaching your computer — it hands the spike to six devices instead of one.
Tell the two apart before you trust one:
- A surge protector states a joule rating. Look on the box, or turn the strip over and read the label on the underside. A number followed by joules — 500, 1080, 2000 — means protective components are inside.
- A surge protector has a status light. Most have a small light marked Protected or Protection Present, next to the power light. A plain power strip has one light at most, and it only tells you the switch is on.
- A plain power strip says nothing at all about protection. If the packaging talks about length, socket count and colour but never mentions joules or surge suppression, that is what it is.
Neither one gives you more electricity. Both draw from the same single wall socket, and the total load is limited by the wiring behind that socket.
2. What a Surge Protector Actually Does
Mains power is not a flat line. It carries spikes — brief jumps in voltage lasting a fraction of a second. Most come from inside your own home, when a fridge compressor, an air conditioner or a laser printer switches on and dumps energy back into the wiring. A lightning strike near the street is the dramatic version, and the rarest.
A surge protector contains components that stay invisible at normal voltage and switch on the instant voltage climbs above a threshold, diverting the excess to the earth wire instead of your laptop's power supply.
That gives you two useful things and one limit:
- It absorbs the small daily spikes that shorten the life of power supplies, chargers and monitors over years rather than seconds.
- It absorbs one large event, up to its rated capacity, which is usually what saves a machine during a storm.
- It does nothing about the power going away. A surge protector holds no energy. When the lights go out, everything plugged into it goes out at the same instant.
3. Joule Ratings, and Why Surge Protectors Wear Out Silently
The joule rating is a lifetime budget, not a per-event threshold. A 1000 joule unit does not survive one thousand-joule hit and then reset. It absorbs energy across its whole life — a hundred joules here, five there — and when the budget runs out, the protective components stop working.
Two consequences that catch people out:
- A higher rating buys longer life, not only more strength. For a desk holding a computer and a monitor, 1000 to 2000 joules is a sensible band. Below 500 joules the budget is spent quickly. Above 3000 joules you are usually paying for a spec you cannot use.
- It fails silently. In most designs the sockets keep delivering power after the protection is gone. Your computer runs perfectly. Nothing beeps. The strip is now an expensive power strip and you have no way of knowing from the outside.
This is what the Protected light exists for. Check it once a month — it is the only warning you get, and on many units the light also goes out if the wall socket has no earth connection, which is worth knowing on its own.
Replace a surge protector every three to five years, and immediately after any lightning strike close enough to hear, a power cut that came back with a bang, or a visible flicker across the whole house. Write the purchase date on the underside in marker when you unbox it. Nobody remembers otherwise.
Manufacturer warranties on connected equipment nearly always require the original receipt and a claim within a set window, so keep the receipt with the box.
4. What a Battery Backup Buys You
A battery backup — sold as a UPS, short for uninterruptible power supply — is a surge protector with a sealed battery inside. When mains power drops, it switches to the battery in a few milliseconds, fast enough that the computer never notices.
Be clear about what that is worth, because the marketing photography tends to imply otherwise:
- It does not buy you a working day. It buys you minutes. The realistic purpose is a calm shutdown: save the file, close the applications, shut down properly, and go and make a coffee until the power comes back.
- It rides out the short stuff. A large proportion of real outages last under thirty seconds — a substation switching over, a storm clipping a line. A battery backup turns those from a lost hour of unsaved work into a beep you look up at.
- It protects against the ugly restart. Power returning is often rougher than power leaving. A machine that was already on the battery never sees that.
- It corrects sagging voltage. Mid-range units include automatic voltage regulation, which quietly steadies brownouts — the dimming that happens when something heavy starts up nearby.
If you work on a laptop, most of this is already handled. The laptop battery is a UPS with a screen attached, and the value of a separate unit is that it keeps the monitor, dock and router alive so the laptop stays usable. For getting more out of the laptop's own battery, see How to Maximize Laptop Battery Life on Windows.
5. Sizing One for a Desk Setup
Sizing sounds technical and is arithmetic. Add up the wattage of everything you want on the battery, then buy a unit rated for at least double that number.
Typical draws for a home office:
| Device | Roughly draws |
|---|---|
| Laptop and its charger | 60–100 W |
| Desktop tower, ordinary office work | 150–250 W |
| Desktop tower with a graphics card | 300–500 W |
| One monitor, 24 to 27 inch | 25–45 W |
| Router and modem together | 15–25 W |
| Dock, external drive, desk phone | 10–20 W |
A laptop, one monitor, a dock and the network gear lands around 150 W. A desktop tower with two monitors lands around 350 W.
Units are advertised with two numbers — VA and watts. Ignore the VA number and read the watt number, which is always the smaller and always the real limit. A unit sold as 900VA / 540W can carry 540 watts.
Buying for double your total is not caution for its own sake. Runtime is not proportional to load: a unit running at half its rated load lasts far more than twice as long as one running flat out. Doubling is what turns "ninety seconds of panic" into "ten minutes and a proper shutdown".
Look for the outlet labels before you buy. Most units split their sockets into two banks, marked Battery Backup + Surge Protection and Surge Protection Only. Only the first bank has the battery behind it. Plugging the computer into the wrong bank is the single most common mistake, and it is invisible until the lights go out.
6. What to Plug In, and What Never To
On the battery bank:
- The computer, or the laptop's charger.
- One monitor. Two if the sizing above allows.
- The router, the modem, and any mesh node in the same room.
- A network drive or external backup drive — an unclean shutdown mid-write is exactly how these get corrupted.
On the surge-only bank, or a separate surge protector:
- Inkjet printers, scanners, speakers, desk lamps, phone chargers.
- Anything you would not miss for the length of an outage.
Never on any bank of a battery backup:
- A laser printer. This is the rule people break. A laser printer's fuser heats to a few hundred degrees and pulls 800 to 1500 watts in short bursts every time it starts a job. That is more than most desk units can supply, so the unit overloads, alarms, and in some cases cuts power to everything including your computer. Give a laser printer its own wall socket and its own surge protector.
- Anything with a heating element or a motor — space heater, kettle, fan heater, vacuum, paper shredder. Same reason, same outcome.
- Another surge protector or power strip. Daisy-chaining defeats the protection, hides the real load from you, and breaches the instructions on nearly every unit sold.
Note: Battery backups contain a sealed lead-acid or lithium battery that dies of old age whether you use it or not, typically after three to five years. Most units self-test and start beeping or showing a Replace Battery indicator when the battery no longer holds charge. Replacement batteries are sold separately and cost a fraction of a new unit.
7. Protect the Router and the Modem Too
A battery backup that carries only the computer solves half the problem. Your laptop stays up, the router goes dark, and you sit looking at a working machine with no connection. For anyone who works from home, network gear on the battery is not optional — it is the point.
What that means in practice:
- Put the router, the modem and the nearest mesh node on the battery bank. Together they draw 15 to 25 watts, so they cost almost nothing in runtime and often keep running for well over an hour after the computer has shut down.
- Fibre connections need the box on the wall too. A fibre service has a small unit where the line enters the building, usually labelled ONT or Optical Network Terminal. If it loses power, the connection stops regardless of what the router is doing. Some come with a small internal battery; most do not.
- Cable and fibre broadband commonly survives a local power cut. The provider's own equipment in the street runs on batteries and generators. The part that failed is your house. Keeping 20 watts of network gear alive is often all that stands between an outage and a normal afternoon.
- Keep a fallback. When the outage is long enough to flatten the battery, your phone's mobile data is the next line — see How to Use Your Phone as a Wi-Fi Hotspot for Your Laptop and set it up before you need it, not during.
If you are building the desk out from scratch, How to Set Up a Home Office Network for Digital Work covers the modem, router and cabling side of the same setup.
Troubleshooting
WARNING
Never plug a laser printer into a battery backup. Its fuser draws 800 to 1500 watts in bursts, which overloads a desk-sized unit and can cut power to everything plugged into it, including the computer you were protecting. Laser printers go in a wall socket, on their own surge protector.
| Symptom / Error | Potential Cause | Solution |
|---|---|---|
| The Protected light on the surge protector is off | Protection spent, or no earth at the socket | Stop using it for computer equipment. Test the same unit in a different wall socket — if the light comes on there, the first socket has an earthing fault and needs an electrician. If it stays off, the strip is finished. |
| Everything on the battery backup died during an outage | Gear plugged into the surge-only bank | Read the labels moulded above each socket. Only the bank marked Battery Backup carries the battery. Move the computer, monitor and router across and test by pulling the wall plug for ten seconds. |
| The unit alarms and shuts off when the printer starts | Laser printer overloading the unit | Move the printer to a wall socket with its own surge protector. A fuser start-up exceeds the capacity of most desk units by a wide margin. |
| Runtime is far shorter than the rating claimed | Load too close to the rated watts, or an aged battery | Recalculate the total load using Step 5 and move non-essential items to the surge-only bank. If the load is well under half the rating and runtime is still short, the battery is at end of life. |
| Constant beeping with everything apparently working | Battery failed its self-test | Look for a Replace Battery light on the front. Order the replacement cartridge for that model — the unit keeps protecting against surges in the meantime, but there is no backup behind it. |
| The computer stayed up but the internet stopped | Router and modem on the wall, not the battery | Move the router, modem and any fibre ONT onto the battery bank. They draw very little and they are what make the remaining runtime useful. |