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Backup Power (UPS)

A used UPS buying guide that goes to 11

Buying a used UPS for your home network or home lab can be a hit-or-miss endeavor. Before deciding to buy a previously owned UPS, please consider these eleven tips:

1) Check battery health and charging history

  • Batteries are the most failure-prone part of a UPS.
  • Ask the seller about the age of the battery and check the manufacture date (usually printed on the battery). Ask when the battery was last charged and if it has ever been replaced.
  • UPS batteries self-discharge over time. If left uncharged for too long (6+ months), they may be permanently degraded.
  • If possible, power on the UPS and verify that it holds a charge. A replacement battery can cost almost as much as a new UPS, so factor this into the price you are willing to pay for the unit.
  • Plug in a test device (e.g., a PC, NAS or a small server) and unplug the UPS power cord from the wall to see if the UPS provides backup power. If the UPS shuts down immediately, the battery may be dead. If not, check how long it can run before depleting the battery, and factor this into the price you are willing to pay for the unit. See Eaton UPS battery runtimes.
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Lithium-ion UPS battery systems

Eaton’s lithium-ion battery systems provide a compact, reliable and flexible solution that ensures 24/7 system uptime while delivering significant total-cost-of-ownership (TCO) savings.

Why lithium-ion?

2) Verify the UPS capacity (VA and wattage rating)

  • Ensure the UPS can manage your power requirements by checking both VA (volt-amps) and wattage.
  • Make sure that the UPS has headroom for future expansion—don’t purchase a UPS that will immediately be supporting its maximum capacity.
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What's the difference between VA and watts?

Our Professor Wattson teaches the importance of understanding the difference between VA versus Watts.

Watch the video

3) Make sure you've got the right wall socket

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  • North America: The maximum UPS load that can be plugged into a standard 120V wall outlet (NEMA 5-15R) is 1500VA (~900W).
  • If you need a higher-capacity UPS, you’ll need a 20A (NEMA 5-20R) or 30A (L5-30R) outlet, which requires an electrician to install. If you plan on using a 240V UPS (common in enterprise setups), you’ll need a 240V outlet (NEMA 6-20R or L6-30R) and, possibly, a subpanel upgrade. Hiring an electrician is recommended to safely install these circuits.

4) Inspect the UPS system's physical condition

  • Look for bulging batteries, corrosion, scorch marks or burnt smells—these are deal-breakers.
  • Check if the fan is excessively loud, as this could indicate wear.
  • Ensure that the display, buttons and LED indicators work properly.
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5. Check the UPS type (standby vs. line-interactive vs. online)

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  • Standby UPS only kicks in when the power fails, but doesn’t regulate voltage.
  • Line-interactive UPS corrects minor voltage fluctuations—good for most home labs.
  • Online (double-conversion) UPS provides the best protection, but consumes more power and generates more heat.

UPS topology 101

When considering different topologies of UPS systems, it’s important to weigh the needs of your environment and the equipment you intend to support.

Choosing the optimal UPS topology

6) Find the user manual and firmware

  • Check to see if the seller is including the original user manual. If not, use your favorite search engine to find it on the internet, as it will be handy in the future in helping with things like firmware upgrades, battery replacement and diagnosing alarms and alerts.
  • Most desktop and network UPS models go through a series of firmware updates throughout their lifespans to correct performance issues. Be sure you have access to the latest firmware from the manufacturer.
  • Check if the manufacturer still supports the model.
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7) Understand component aging: capacitors and fans wear out

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  • UPS capacitors degrade over time, even if the UPS wasn’t heavily used. A UPS that’s more than 7-10 years old might need capacitor replacement, which can be difficult without proper tools.
  • Fans in older UPS units can become noisy or fail, leading to overheating and shutdowns. If the fan is excessively loud, consider it a signal that it may need replacing soon.
  • Unlike consumer electronics, UPS manufacturers typically do not sell individual components like capacitors or fans. Nor do they provide the electrical design diagrams, due to the inherent electrical dangers and liability concerns associated with high-voltage electronics.
  • If you plan to repair a UPS, you’ll need to source third-party components and work at your own risk.

8) Look for network and remote management features

  • Some UPS units come with a network management card (NMC) for remote monitoring. Confirm full functionality of any NMC your UPS includes.
  • Verify whether the UPS supports USB, serial or network-based management, depending on your needs.
  • If you plan to use software, check the compatibility before buying.
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UPS power management solutions

Whether you need to monitor a single UPS or monitor an entire data center, Eaton has the power management software solution for you.

Find your solution

9) Does the UPS have the right number and type of outlets?

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  • Add up the number of pieces of equipment that your UPS will need to support, and make sure that the UPS has enough outlets to accommodate them.
  • Also, make sure that the UPS has the right type of outlets for potential supported equipment.
  • Finally, some UPS models have both battery and surge-protected outlets, as well as surge-only outlets that will not provide battery power during an outage. Consider what equipment will need which kind of UPS protection. 

10) If buying a rack-mount UPS, consider the mounting hardware

  • Many used rack-mount UPS units are sold without the original rack ears, brackets or rails.
  • Make sure the seller includes the mounting hardware, or check whether replacements are available for your model.
  • Consider the weight. A rack-mount UPS is heavy (often 40-80 pounds), so ensure that your rack can support it.
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11) Price vs. value: is it worth it?

  • Add up the cost of a used UPS + potential new battery—it may be less expensive to buy new.
  • Sometimes, a refurbished UPS with a fresh battery from a reputable seller is a better deal than buying used from an individual.
  • Factor in additional expenses such as potential repairs, battery replacements and software licensing (for smart UPS models).
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Check out the current Eaton UPS portfolio

Eaton UPS systems deliver high quality, reliable backup power for everything from network closets and server rooms to enterprise and colocation data centers.

Browse our selection
Eaton is an intelligent power management company dedicated to improving the quality of life and protecting the environment for people everywhere. We are guided by our commitment to do business right, to operate sustainably and to help our customers manage power ─ today and well into the future. By capitalizing on the global growth trends of electrification and digitalization, we’re accelerating the planet’s transition to renewable energy and helping to solve the world’s most urgent power management challenges.
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