Frequently Asked Questions

The five questions we hear most

What size UPS do I need?

Add up the real watts of the devices that need battery power (not their power supply labels), then choose a UPS whose watt rating is at least 25% higher. Check runtime at that load. The UPS sizing calculator does this for you.

How long will my UPS last in an outage?

It depends on load far more than on the VA rating. A typical 1500 VA unit lasts a few minutes at full load and roughly an hour at 100 W. Try the runtime calculator.

How often should I replace the battery?

Usually every 3 to 5 years for sealed lead-acid batteries, sooner in warm rooms. Replace when the UPS reports a failed self-test or runtime falls below what you need. See when to replace a UPS battery.

Do I need pure sine wave output?

For modern computers with active-PFC power supplies, gas furnaces and anything with a motor, pure sine is strongly recommended. Simple loads like routers and laptop chargers are fine on simulated sine. See pure vs simulated sine wave.

Can I plug a UPS into a surge protector?

Manufacturers say no, and so do we. Plug the UPS directly into a wall outlet. See UPS and power strips.

UPS Fundamentals

• How long will a UPS keep my computer running? (What Is a UPS? How an Uninterruptible Power Supply Works)
• Is an online UPS always better than a line-interactive one? (UPS Types Explained: Standby vs Line-Interactive vs Online)
• How many watts is a 1500 VA UPS? (VA vs Watts: How to Read a UPS Rating Correctly)
• Will a simulated sine wave UPS damage my PC? (Pure Sine Wave vs Simulated Sine Wave: Which UPS Output Do You Need?)
• Does a UPS with AVR use the battery during a brownout? (Automatic Voltage Regulation (AVR): How a UPS Fixes Sags Without the Battery)
• What is a good UPS transfer time? (UPS Transfer Time: Why a Few Milliseconds Usually Don't Matter (and When They Do))
• Does a UPS replace a surge protector? (UPS vs Surge Protector: What Each One Actually Protects)
• Why does my UPS have outlets that do not work during a power outage? (UPS Outlets and Plugs: Battery vs Surge-Only, NEMA and IEC)
• Do I need a pure sine wave UPS for an active PFC power supply? (Active PFC Power Supplies: What They Are and Why Your UPS Cares)
• What does VFI-SS-111 mean on a UPS spec sheet? (UPS Specifications Explained, Line by Line)
• What size UPS do I need for a home computer? (UPS Buying Guide: How to Choose the Right UPS)

Sizing & Runtime

• What size UPS do I need for a desktop computer and one monitor? (How to Size a UPS: A Step-by-Step Method That Works)
• How accurate is a Kill A Watt style meter? (How to Measure the Power Draw of Your Equipment)
• Is it bad to run a UPS at 90% load? (UPS Load Percentage: What the Number Means and Where It Should Sit)
• Why does my UPS say 40 minutes of runtime but shut off after 15? (UPS Runtime Explained: Why Double the Load Gives Less Than Half the Time)
• Is 5 minutes of UPS runtime enough? (How Much UPS Runtime Do You Actually Need?)
• Can I add an external battery to any UPS? (Extended Runtime Battery Packs: Adding Hours, Not Just Minutes)
• Does a UPS use electricity when nothing is plugged in? (UPS Efficiency and Energy Cost: The Real Running Cost of Backup Power)
• What size UPS do I need for an 850 W power supply? (Sizing a UPS for a Gaming PC: Watts, Spikes and Runtime)

UPS Batteries

• Are UPS batteries the same as car batteries? (UPS Battery Types: VRLA AGM, Gel, Flooded, LiFePO4 and Li-ion)
• Can I use a 12V 9Ah battery instead of a 12V 7Ah in my UPS? (UPS Battery Sizes and Terminals: Case Sizes, F1/F2 Tabs and Series Strings)
• How long does a UPS battery last on average? (UPS Battery Lifespan: Design Life, Real Life and the Heat Penalty)
• Can a UPS battery go bad if the power never goes out? (When to Replace a UPS Battery: Warning Signs and Practical Tests)
• Do I need to turn off the UPS to change the battery? (How to Replace a UPS Battery: A Safe, Step-by-Step Guide)
• Can a swollen UPS battery explode? (Swollen UPS Battery: What It Means and What to Do Right Now)
• Will an aftermarket battery void my UPS warranty? (OEM vs Aftermarket UPS Batteries: What You Are Really Paying For)
• Can I put a LiFePO4 battery in my existing UPS? (Lithium UPS Pros and Cons: When LiFePO4 Pays Off)
• How long can a UPS sit unplugged before the battery is ruined? (How to Store a UPS and Spare UPS Batteries)
• Do auto parts stores take small UPS batteries? (UPS Battery Recycling: Where to Take Old Lead-Acid and Lithium Batteries)

Power Quality & Surge Protection

• What is the most common power problem in a home? (Power Problems Explained: The Nine Disturbances and What Fixes Each)
• Why do my lights dim when the air conditioner turns on? (Brownouts and Voltage Sags: What Low Voltage Does and How to Stop It)
• Can a surge protector stop a direct lightning strike? (Lightning and Surges: How They Reach Your Equipment and What Actually Helps)
• How many joules do I need in a surge protector? (Surge Protector Ratings Explained: What Joules, VPR and MCOV Really Tell You)
• Do I still need surge strips if I have a whole-house surge protector? (Whole-House Surge Protection: Types, Code Requirements and Layering)
• Should I plug a power conditioner into a UPS or the UPS into a power conditioner? (Power Conditioners Explained: What the Label Really Means)
• Is it safe to keep using a UPS with the site wiring fault light on? (Site Wiring Faults, Grounding and Your UPS)
• What is a good THD for a UPS? (Harmonics and THD: What the Numbers Mean for a UPS)
• What voltage should a US wall outlet read? (Measuring Power Quality at Home: Tools, Readings and a Diagnostic Plan)

Use Cases

• Will a UPS reduce my frame rate or gaming performance? (UPS for a Gaming PC: Protecting the Whole Setup)
• Can I just plug my laptop into a UPS? (UPS for a Home Office: Staying on the Call When the Power Drops)
• How long will a 600 VA UPS run a modem and router? (UPS for a Modem, Router and Fiber ONT: Keeping the Internet Up)
• Does a landline work during a power outage? (UPS for VoIP and Home Phones: Keeping a Dial Tone (and 911) in an Outage)
• Can a power outage damage a PS5 or Xbox? (UPS for a Home Theater and Game Consoles: What Belongs on Battery)
• Does a Synology or QNAP NAS need a pure sine wave UPS? (UPS for a NAS: Protect Your Data, Shut Down Cleanly, Come Back Automatically)
• How long should a homelab UPS run? (UPS for a Homelab Server, Proxmox Host or Mini PC Cluster)
• Do I need an online double-conversion UPS for a network rack? (Choosing a UPS for a Small Business or Homelab Network Rack)
• Will my security cameras record during a power outage? (UPS for Security Cameras, NVRs and DVRs: Keep Recording When the Power Is Cut)
• Can I still take card payments during a power outage? (UPS for a Small Business Point of Sale: Keeping Payments Running)
• Does a 3D printer need a pure sine wave UPS? (UPS for a 3D Printer: Riding Through Outages vs Saving the Print)
• Why does my furnace work on utility power but lock out on a generator or inverter? (Running a Gas Furnace on a UPS: What Works and What Fails)
• How many watts does a refrigerator need to start? (Can a UPS Run a Refrigerator? The Math Says Rarely)
• Can a 1500 VA UPS run a 1/3 HP sump pump? (Sump Pump Backup: Why a Computer UPS Is the Wrong Tool)
• How long can fish survive without a filter or air pump? (Aquarium Battery Backup: Keep the Air and Water Moving, Not the Heater)
• Does the California garage door law apply to my existing opener? (Garage Door Opener Battery Backup: UPS or Built-In Battery?)
• Can I plug my CPAP into any UPS? (Backup Power for a CPAP: UPS, DC Battery or Both?)
• Can I run an oxygen concentrator on a UPS? (Backup Power for Home Medical Equipment: Start With the Maker)

Troubleshooting & Alarms

• Why is my UPS beeping when the power is not out? (Why Is My UPS Beeping? What the Beep Patterns Usually Mean)
• Can I keep using a UPS with the replace battery light on? (UPS Replace Battery Light On? How to Confirm It and Clear It)
• Why does my UPS say overload only when the power goes out? (UPS Overload Alarm: Find the Load That Is Too Big and Fix It)
• Why won't my brand new UPS turn on? (UPS Won't Turn On? Work Through These Checks in Order)
• How long should a new UPS charge before first use? (UPS Not Charging: How to Tell a Dead Battery From a Failed Charger)
• Is it safe to keep using a UPS with the site wiring fault light on? (UPS Site Wiring Fault Light: Causes, Tests and Fixes)
• Is it bad if my UPS switches to battery several times a day? (UPS Keeps Switching to Battery? How to Find the Cause)
• Why does my UPS work in a self test but fail during a real outage? (UPS Shuts Off When the Power Goes Out: Causes and Fixes)
• Why does my UPS click back and forth between battery and generator? (UPS Won't Accept Generator Power? How to Diagnose It)
• Why does my UPS click when nothing seems wrong with the power? (UPS Buzzing or Clicking: Which Noises Are Normal and Which Mean Trouble)
• Why does my new UPS only last a few minutes? (Why Your UPS Runtime Is Shorter Than Expected (and How to Fix It))
• Can I use a regular Ethernet cable in the UPS data port? (UPS Not Detected by Your Computer: How to Fix It)
• Is it safe to keep using a UPS that smelled burnt once but seems fine now? (UPS Running Hot or Smelling Burnt: Safety First, Then Diagnosis)

Installation & Maintenance

• Can I use a new UPS right away without charging it first? (How to Set Up a UPS: Step-by-Step From Unboxing to First Test)
• Can I put a UPS on the floor? (Where to Place a UPS: Ventilation, Temperature and Location Rules)
• Will plugging my UPS into a surge protector void the warranty? (Plugging a UPS Into a Power Strip, Surge Protector or Extension Cord)
• Do home UPS units need professional maintenance? (UPS Maintenance Checklist: What to Check and How Often)
• Why did my UPS pass the self-test but die quickly in a real outage? (UPS Self-Test vs Runtime Calibration: What Each Does and How to Run Them)
• Can I mount a rack UPS using only the front ears? (Rack-Mount UPS Installation: A Practical Guide)
• What size generator do I need to run a 1500 VA UPS? (Using a UPS With a Generator: How to Plan a Setup That Works)
• Can I plug a UPS with a 5-20P plug into a normal outlet? (Hardwired vs Plug-In UPS: Plugs, Circuits and When to Call an Electrician)
• Can I throw an old UPS in the trash? (UPS End of Life: Retire, Wipe, Recycle)

Software & Monitoring

• Do I need to install UPS software at all? (UPS Software: What It Does and Which Tool to Use)
• Can I use PowerPanel with an APC UPS or PowerChute with a CyberPower UPS? (PowerChute and PowerPanel: Vendor UPS Software Explained)
• What port does NUT use? (Network UPS Tools (NUT): A Complete Setup Guide)
• Does apcupsd work with CyberPower or Eaton UPS units? (apcupsd: Configuring APC UPS Monitoring and Shutdown)
• Why does Windows show my desktop PC as having a battery? (Automatic UPS Shutdown on Windows Without Extra Software)
• Why do I not see UPS options on my Mac? (Setting Up a UPS on a Mac: Shutdown Options and pmset)
• Does Synology work with APC, CyberPower and Eaton UPS units? (Synology NAS UPS Setup: USB, Network UPS Server and NUT Clients)
• Which driver should I pick for my UPS in TrueNAS? (TrueNAS UPS Setup: The UPS Service, Shutdown Modes and Remote Clients)
• Does Unraid work with CyberPower or Eaton UPS units? (Unraid UPS Setup: Built-in apcupsd, the NUT Plugin and Shutdown Timing)
• Should I pass the UPS USB device through to a VM? (Proxmox VE UPS Shutdown: NUT on the Host and Getting the Order Right)
• Do I need the NUT add-on or just the integration? (Monitoring a UPS in Home Assistant: NUT Integration, Add-on and Automations)
• Do I need a network management card for my UPS? (UPS Network Management Cards and SNMP Monitoring)

Brands & Product Lines

• Is APC Back-UPS pure sine wave? (The APC UPS Lineup: Back-UPS, Smart-UPS, SRT and Easy UPS Explained)
• Is the CyberPower Intelligent LCD series pure sine wave? (The CyberPower UPS Lineup: Standby, AVR, PFC Sinewave, Smart App and OL)
• What is the difference between Eaton 5S and 5SC? (The Eaton UPS Lineup: What 3S, 5S, 5SC, 5P/5PX and 9SX/9PX Mean)
• Is Tripp Lite the same as Eaton now? (The Tripp Lite UPS Lineup: SMART, SmartPro, OmniSmart, SmartOnline and More)
• Is Liebert the same company as Vertiv? (Vertiv Liebert UPS Lineup: PSI5, GXT5, GXT4 and Beyond)
• Does the 1500 in a UPS model number mean 1500 watts? (How to Read UPS Model Numbers: A Practical Decoder)
• Does a UPS warranty cover the battery? (UPS Warranties and Equipment Guarantees: What They Really Cover)

Comparisons

• Is an online UPS worth it for a gaming PC? (Line-Interactive vs Online (Double-Conversion) UPS)
• Is a standby UPS good enough for a modem and router? (Standby (Offline) vs Line-Interactive UPS)
• Can I use a portable power station as a UPS for my computer? (UPS vs Portable Power Station for Home Backup)
• Is APC or CyberPower more reliable? (APC vs CyberPower: Which UPS Family Fits Your Job?)
• Is Eaton 5PX comparable to APC Smart-UPS? (Eaton vs APC: Comparing UPS Families for Office, Closet and Rack)
• Can I put a lithium battery in my lead-acid UPS? (Lead-Acid vs Lithium UPS: Which Battery Chemistry Wins?)
• Can I lay a rackmount UPS flat on a shelf without rails? (Rack vs Tower UPS: Choosing the Right Form Factor)
• Can a UPS replace a generator for a long outage? (UPS vs Generator: Instant Ride-Through vs Long-Duration Power)
• Can one DC mini UPS power both my modem and my router? (DC Mini UPS vs AC UPS: Which Keeps Your Internet Up Longer?)

Calculators & Tools

• What size UPS do I need for a desktop computer and monitor? (UPS Sizing Calculator)
• How long will a 1500 VA UPS last? (UPS Runtime Calculator)
• How do I convert VA to watts? (VA to Watts Converter)
• How long does a UPS battery last? (UPS Battery Life Estimator)
• How much electricity does a UPS use? (UPS Energy Cost Calculator)
• Why is my UPS beeping when the power is on? (UPS Alarm Decoder)

Data & Reference

• How many watts does a gaming PC use? (Device Power Draw Database)
• Can I replace a 12 V 7 Ah UPS battery with a 12 V 9 Ah one? (UPS Battery Reference Table)
• Which UPS type is best for home use? (UPS Topology Comparison Table)
• Can I plug a UPS with a NEMA 5-20P plug into a normal outlet? (Plug and Receptacle Reference for UPS Systems)

Can't find your question? Try the glossary, browse the troubleshooting guides, or ask us.