UPS glossary
Plain explanations of the parts and terms you'll see on a UPS, its label, and its battery. For setup and design choices, see the UPS guides.
Batteries
- Battery cartridge
- APC's name for a ready-to-fit replacement battery. It's usually one or more batteries already wired together with their connector, so you swap the whole unit. Our pages call it the battery.
- RBC (replacement battery cartridge)
- The start of APC's cartridge part numbers, such as APCRBC124. You can search for one of these codes here as well as the UPS model.
- Battery pack
- A general name for several batteries joined together. CyberPower's replacement battery codes start with RB, such as RB1290X2.
- External battery pack
- An extra battery box that plugs into some UPS models for longer runtime. Eaton calls it an external battery module (EBM). It's sold separately from the replacement battery inside the UPS.
- Sealed lead-acid (SLA or VRLA)
- The most common battery type in a UPS. It's sealed, so it never needs topping up. Most use AGM (absorbent glass mat), where the acid sits in a fiber mat rather than as free liquid.
- Lithium-ion
- Some newer UPS models use lithium-ion batteries, which are lighter and tend to last longer. Please don't swap lead-acid for lithium-ion, or the other way round, unless the manufacturer says you can.
- User-replaceable
- The manufacturer says you can change the battery yourself, usually through a door or panel. If your model isn't user-replaceable, contact the manufacturer for service.
- Hot-swappable
- You can change the battery while the UPS stays on and keeps powering your equipment. Only do this if your manual says the model supports it.
- Terminals and connectors
- The metal tabs where the battery wires attach, often called F1 or F2 by size. Please don't bridge them or connect them a different way.
- Wiring harness
- The cables and plug that join the batteries in a cartridge and connect them to the UPS.
- Battery life
- Most UPS batteries last a few years. Heat and frequent outages wear them out faster. The replace battery warning and your manual are the best guide.
- Recycling
- Old UPS batteries shouldn't go in the trash. Take them to a battery recycling point or a store that accepts them.
Inside the UPS
- UPS (uninterruptible power supply)
- A box that keeps your equipment running for a short time when the power goes out, and protects it from spikes and dips. Inside are a battery, a charger, and an inverter.
- Inverter
- The part that turns the battery's DC power into the AC power your equipment uses.
- Charger
- Keeps the battery topped up while the UPS is plugged into the wall.
- AVR (automatic voltage regulation)
- Corrects high or low wall voltage without switching to battery, which saves wear on the battery.
- Standby UPS
- Switches to battery only when the power fails. Common in small, low-cost units. Also called offline.
- Line-interactive UPS
- A standby design with AVR added. Popular for home offices and small network gear.
- Online UPS
- Runs your equipment from the inverter all the time, so there's no switch-over when the power fails. Used for servers and sensitive equipment. Also called double-conversion.
- Sine wave
- A smooth, repeating curve that describes how AC (wall) power rises and falls many times each second. Think of the gentlest possible up-and-down motion — not a sharp square or a set of steps. Wall outlets deliver a sine wave. UPS makers talk about sine waves because, on battery, the UPS has to recreate that shape.
- Pure and simulated sine wave
- When the UPS runs on battery, it makes its own AC power. Wall power is a smooth wave (a pure sine wave). A pure sine wave UPS copies that smooth shape. A simulated (or "stepped") sine wave UPS makes a rough, blocky version of it. Many computers and monitors are fine with either. Some computers, audio gear, and laser printers prefer or need a pure sine wave. Check your UPS manual or the label on the equipment if you're unsure.
- Transfer time
- How long the UPS takes to switch to battery when the power fails. It's usually a few milliseconds. An online UPS has none.
- Self-test
- A short check the UPS runs on its battery, either on a schedule or when you press a button. A failed self-test often sets off the replace battery warning.
- Replace battery warning
- A light, beep, or screen message saying the battery failed a test or is near the end of its life. It doesn't tell you which battery to buy.
Ratings and power
- VA (volt-amperes)
- The UPS's size rating, such as 1500 VA. It's often the number in the model name.
- Watts
- How much power the UPS can actually supply. It's lower than the VA figure, and it's the number to compare with what your equipment needs.
- Load
- The total power drawn by everything plugged into the battery outlets. More load means less runtime.
- Runtime
- How long the UPS can keep your equipment running on battery. It depends on the load and the battery's age.
Outlets, cables, and add-ons
- Battery backup outlets
- The outlets that stay on during an outage. Plug in the things that must keep running, like a computer, router, or modem.
- Surge-only outlets
- Outlets protected against spikes but not backed by the battery. Fine for things like printers that don't need to stay on.
- C13 and C14 connectors
- The connectors used on computer power cords and rack equipment. Many rack-mount UPS models have C13 outlets instead of household sockets.
- USB or serial cable
- Lets the UPS tell your computer the power is out, so it can shut down safely using the manufacturer's software.
- Network management card
- An add-on card that lets you check and control the UPS over a network.
- Rack-mount and tower
- A tower UPS stands upright on the floor or a shelf. A rack-mount UPS fits a standard 19-inch equipment rack, often on rails.
- PDU (power distribution unit)
- A strip of outlets for an equipment rack, often plugged into a UPS.
On the label
- Model number
- Printed on the label on the back or bottom of the UPS. It's what you search for here, rather than the code on the old battery.
- Serial number
- A unique code on the same label. For a few models, the first three characters (the serial prefix) decide which battery fits.
- Region suffix
- Letters at the end of a model, like -CN, that mark a regional version. It can change the battery, so include it when you search.