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August 30, 2021

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10 min

UPS Battery Backup Buying Guide: What You Need to Know

Prepare yourself with our uninterruptible power supply (UPS) battery backup buying guide to help you choose the best UPS for your needs, so you can be ready for the worst.

You don’t know how necessary an uninterruptible power supply (UPS) is until the power goes out and your expensive equipment is fried, your valuable data is lost and system downtime causes serious negative revenue impacts. Prepare yourself with our UPS battery backup buying guide to help you choose the best UPS for your needs so you can be ready for the worst.

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What is an Uninterruptible Power Supply (UPS)?

A UPS serves three basic roles: a backup batterysurge protector and power inverter. The backup battery and power inverter supplies power to your connected electronics in the event of a power outage, fluctuation or other disturbance. A UPS also guards against voltage spikes/surges, frequency noise/variation, harmonic distortion, and more, depending on the type of UPS you buy.

Why You Need a UPS

The reason you need a UPS is that electronic devices are oftentimes expensive, and you should always expect the unexpected. A UPS is an effective solution for wireless networking equipment, computers, TVs, gaming consoles, servers and basically anything else that gets plugged into a standard power outlet.

Voltage spikes can easily damage plugged-in hardware, even if they occur for just a few nanoseconds. The excess electricity causes overheating, breaks and cracks in wires, frying circuit boards, hard drives and most other electrical components.

The backup battery in a UPS allows you to save/back up your data and shut down your sensitive electronic devices safely and/or avoid downtime altogether. For instance, the power capacity of the backup battery can buy you enough time to spin up power generators or supply power long enough until AC power is restored.

Common Power Problems

There are several common power issues a UPS can help protect you against:

  • Blackout. Probably the issue that’s most familiar, this is the complete loss of electrical supply due to utility equipment/power grid failure, natural disasters or human error. Blackouts can last from a few seconds to a few days.
  • Brownout. Also known as a voltage dip or under voltage, occasionally electricity is still reaching your electronic devices, but at reduced voltage, for an extended amount of time. Rarer than blackouts, oftentimes this happens due to compromised power resources or reduced power flow in high demand circumstances.
  • Frequency Variation. This is a problem that can arise when connected to power generators, when the generator is no longer synced to the power system within a desired frequency.
  • Harmonic Distortion. Caused by electronic devices (including UPS systems themselves) drawing current in jagged pulses rather than a smooth, sinusoidal wave.
  • Line Noise. Also called frequency noise, line noise is caused by interference of stray electromagnetic signals within a standard AC current, line noise can be caused by other AC-connected electronic devices, radio wave interference, power generators, or lightning storms. It can hinder the performance of electronic circuits.
  • Overvoltage. Basically a mini power surge, also known as a swell, this is higher-than-normal voltage lasting longer than a surge. It could last a few minutes or even several days.
  • Power Surge/Spike. Also called “transient voltage”, this is a brief, unexpected increase in voltage outside normal limits for wall outlets (typically 0 and 169 volts, or greater than 110% of normal output). Lightning strikes can bring about huge power surges that damage or destroy devices instantly. Even small surges from faulty contactors can cause permanent damage over time.
  • Voltage Sag. A type of brownout that is shorter in duration.

What Kind of UPS is Best for You?

The best UPS for you will depend on these factors:

  • The power problems you’re trying to avoid (see the above section)
  • The number of electronic devices you’re looking to support with the UPS
  • The wattage of the electronic devices you’re connecting to the UPS
  • How long you need the backup battery to run for, or runtime
  • Form factor/how much space you have for the UPS

Types of UPS Systems

There are 3 fundamental types of UPS systems: standby, line interactive and double conversion, which all come in various capacities.

Standby UPS

Also known as an offline UPS or VFD (Voltage and Frequency-Dependent) UPS, is the most common type of UPS system, offering basic power protection and backup battery capabilities. Standby UPSs defend against blackouts as well as both voltage surges and spikes. However, they aren’t capable of regulating power dips and transient voltage. For that you would need at least a line-interactive UPS.

 In the event of the main power supply dipping above or below the normal limits, the load is transferred to the inverter output, typically within 5-8 milliseconds. They are called “offline” or “standby UPS” since the inverter is switched off by default. Generally, offline UPSs provide a square/pseudo sine wave output waveform, which can be problematic in combination with sensitive electronic equipment. Square/pseudo sine waves can cause overheating, malfunctioning or even equipment failure in some electronics.

Most of these units only run for 5-20 minutes to give you enough time to properly shut off your computer so you’d need to upgrade to a UPS with a larger capacity if this won’t meet your needs. Standby UPSs are best-suited for small, non-critical electronic devices and home/personal office use.

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Line-Interactive UPS

Line-interactive UPS systems are the next step up in power protection and cost from standby UPSs. With this type of UPS, the inverter is always on and connected to the UPS output. Line-interactive UPSs have automatic voltage regulation (AVR), using transformers to keep the voltage within set low/high limits (usually plus or minus 8-15% of the nominal voltage). Whereas a standby UPS would switch to battery power in such an instance, line-interactive UPS systems do not. This conserves battery power in the short-term as well as the battery life in the long-term.

Unlike standby UPS systems, the inverters of line-interactive UPS systems are part of the output and always connected. While the input AC power is flowing normally, the inverter is reversed and charges the battery. If the input AC power fails, the transfer switch changes direction within about 4-8 milliseconds, allowing the battery power to flow to the UPS output. These few milliseconds, while a quick enough transfer for most equipment, may not cut it for very sensitive electronics, so you may need to look to online UPSs.

In the event of a power failure, most line-interactive UPS systems deliver pure sine wave output, making them a good pairing with most devices. Also, most line-interactive UPSs can power up to 4,000 watts of connected equipment. Beyond that, you should investigate online UPSs.

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Online UPS

Also called an online double-conversion UPS, online UPS systems provide the highest level of protection for IT equipment in hospitals and data centers. They are called double conversion because they convert the incoming AC power to DC, and then take that DC power and convert it back to AC output via the inverter.

Online UPSs prevent any power delivery irregularities, defending against all potential power issues and deliver continuous, consistent power and protection in the event of a power outage, surge, dip, or any of the common power issues outlined in the above section. They are also ideal for “cleaning up” power from generators, smoothing out any irregularities in the sine wave. This makes online UPSs great for use in data centers using backup generators.

The output regulation is also much more precise than line-interactive UPSs, keeping the nominal voltage plus or minus 2-3%, ensuring that connected electronics are not damaged by over- or under-voltage. Also, because online UPSs consistently supply AC power to connected electronics, there is no downtime whatsoever in the event of an outage, unlike standby and line-interactive UPS systems.

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Selecting a UPS System by Capacity/Runtime

No matter what type of UPS system you buy, you’ll need to make sure it has enough capacity to support the wattage of the devices you plug into it, as well as enough battery runtime to shut down safely. It’s important to account for the number of plugs your UPS has as well.

Simply tally up the wattage of every device you plan to connect your UPS to (this is your load) and multiply that number by 1.25 to determine the UPS capacity you need. Your load should not exceed 75%-80% of your UPS system’s capacity. Then just make sure the number of plugs is greater than or at least equal to the number of devices you plan on connecting to your UPS.

Keep in mind a UPS will never support its full capacity, and the closer you get to capacity, the less battery runtime you will have. Plan for how much time you need to safely shut down your connected devices and account for this when considering how much capacity you need for your UPS system. Also, some UPS manufacturers offer extended battery modules (EBMs) to extend total runtime if that is a concern.

Selecting a UPS System by Form Factor

How much space you have is also an important factor when selecting a UPS battery backup. These are the three primary form factors for UPS systems:

  • Desktop/Compact UPS. Also known as a low-profile or flat-pack UPS, these UPSs are short and wide and can fit on a desk, under a desk or be tucked into a cubbyhole easily. Most models also feature mounting slots on the back if you’re looking to conserve space and mount it to the wall.

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  • Tower/Mini-Tower UPS. These are taller, narrower UPSs with outlets on the backside of the device. They stand upright and can be placed on a desk, shelf or on the floor. If you’re looking for a UPS for your server room, a rackmount UPS may be the best way to conserve space. You can also store your tower UPS in a 2 or 4 post rack to avoid accidental damage or unplugging.

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  • Rackmount UPS. These UPSs are for mounting within standard 19” server rack enclosures alongside other IT equipment to conserve space. They take up anywhere from 1U to 14U of vertical rack space and are typically designed to be configured horizontally.  Standard server racks are 42U, with each unit (U) being 1.75” high, with common rackmount UPSs found in 1U, 2U or 4U sizes.

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Secondary UPS Features

There are several additional UPS features to consider other than the major considerations outlined above.

  • Software/OS. Some UPSs feature software that allow them to interface with your computer, depending on your computer’s OS, particularly with higher-end UPSs. For instance, APC offers a software called PowerChute safe system shutdown software, or CyberPower’s PowerPanel for local or remote UPS monitoring and management.
  • Available Connections. Not every outlet on every UPS offers battery backup and surge protection. Ensure that there are enough outlets that can support the devices you need backup battery power for. Some UPS battery backups also offer surge protection for ethernet and coax cable in case you’re interested in using your UPS for a cable modem and/or router.
  • LCD Displays. Some UPSs have LCD screens which show you battery/power conditions and help you control the UPS directly. It can be a nice alternative to screenless UPSs, which oftentimes will beep as an alert without indicating what is wrong.
  • Remote Monitoring and Management. Higher-end UPSs tend to offer both local and remote UPS monitoring so you can get insight into run-time, battery health and other important factors through an easy-to-use software interface.
  • Replacement Batteries. You will want to look in whether you can replace the UPS battery or not once it has run its lifespan. This can mean the difference between buying a new UPS versus buying just a new battery. You’ll want to consider this when buying lower cost UPS units particularly, since these models tend to not have replaceable batteries.
  • Lithium-Ion (Li-ion) vs. Lead Acid Batteries. The use of lithium ion batteries in UPS systems is a relatively new concept; however, lead acid batteries are still the dominant battery type used in UPS systems. Li-ion batteries provide longer life spans, less weight, faster recharge times and more. It may be worth your while to look for a UPS battery backup with a li-ion battery.
  • Energy-Saving Features. Some UPS battery backups are Energy Star-certified and reduce energy waste by up to 52% versus non-Energy Star-certified UPSs. Some UPSs offer “eco-modes” or “active standby”. For line-interactive and online UPSs, these energy-saving modes are like how offline UPSs work, with the inverter on standby until there’s a power issue.

We hope this has guided your UPS buying decision. CDW offers UPS battery backups from all the top brands, including APC, CyberPower, Eaton, Tripp Lite, Vertiv and more. Whether you need to backup your home office or your data center, we get that backing up your work is vital.