UPS Battery BackupsLine-Interactive
CyberPower CST135UC2 UPS Battery Backup Manual
Setup, everyday use, maintenance and troubleshooting for the 1,200 VA / 800 W line-interactive UPS, with verified specifications.
- Rating1,200 VA / 800 W
- TopologyLine-Interactive
- Efficiency98.7%
- Runtime at half load11 min
About the CyberPower CST135UC2
CyberPower model CST135UC2 is a 1,200 VA / 800 W line-interactive UPS that meets ENERGY STAR UPS efficiency requirements.
It can support up to 800 W of connected equipment (1,200 VA apparent power, a 0.67 output power factor), expandable to 900 W in its maximum configuration. It is rated for 110–120 V, 60 Hz input and 120 V output. It has 8 outlets: 4 with battery backup and surge protection and 4 with surge protection only. Energy storage is a valve-regulated lead-acid (VRLA) battery (internal), with a 3-year warranty listed in the certification record.
ENERGY STAR weighted efficiency is 98.7%, and 98.7% at half load. With nothing connected it draws 3.38 W. Its weighted efficiency is higher than 41% of the 288 Line-Interactive models in our database.
The manufacturer lists it for consumer and commercial applications.
Specifications
| Brand | CyberPower |
|---|---|
| Model number | CST135UC2 |
| Topology | Line-Interactive |
| Apparent power rating | 1,200 VA |
| Real power rating | 800 W |
| Maximum configuration rating | 900 W |
| Output power factor (W/VA) | 0.67 |
| Default normal mode | VI (voltage independent) |
| Intended applications | Consumer, Commercial |
| Rated input voltage | 110–120 V |
| Rated output voltage | 120 V |
| Input frequency | 60 Hz |
| Total outlets | 8 |
| Battery backup + surge outlets | 4 |
| Surge-only outlets | 4 |
| Battery technology | Valve-regulated lead-acid (VRLA) |
| Battery location | Internal |
| Runtime at full load | 3 min |
| Runtime at half load | 11 min |
| Battery warranty | 3 years |
| Weighted efficiency (ENERGY STAR) | 98.7% |
| Efficiency at 25% load | 98.1% |
| Efficiency at 50% load | 98.7% |
| Efficiency at 75% load | 98.7% |
| Efficiency at 100% load | 98.7% |
| Input power at no load | 3.4 W |
| Input power factor | 1.00 |
| Rack-mountable | No |
| Height | 9.8 in. |
| Width | 3.9 in. |
| Depth | 13.7 in. |
| Modular design | No |
| Communication ports | USB, Ethernet |
| Manufacturer take-back program | No |
Safety information
- Plug the UPS directly into a properly grounded wall outlet. Do not plug it into a surge protector, power strip or extension cord, and do not plug a power strip or surge protector into its battery outlets unless the manufacturer explicitly allows it.
- Do not connect laser printers, space heaters, hair dryers, vacuum cleaners or other high-current appliances to the battery outlets; their surge current can overload the UPS.
- The UPS contains a battery that can deliver dangerous energy even when the unit is unplugged, and its outlets may be live on battery power. Do not open the enclosure except to replace batteries as described in the manual.
- Install the UPS indoors in a clean, dry, well-ventilated location away from heat sources and direct sunlight. High temperatures shorten battery life sharply.
Installation and first-time setup
Size the load first. Add up the wattage of the equipment you plan to protect (check each power supply label or measure it with a plug-in meter). Keep the total below the 800 W rating — ideally under about 640 W (80%) to leave headroom for start-up surges and battery aging. The 1,200 VA figure is apparent power; the watt rating is the one that limits most modern IT equipment.
- Inspect and position
Unpack the UPS and check for shipping damage. Place it on a hard, level surface with the ventilation openings unobstructed.
- Connect the battery
Many UPS units ship with the battery disconnected for safety. If so, connect it as shown in the quick-start guide before plugging in.
- Connect input power
Plug the UPS into a grounded wall outlet on a circuit that is not heavily loaded by other equipment.
- Charge the battery
Turn the UPS on and let it charge for several hours before relying on full runtime. Equipment can be connected and used during charging, but runtime will be limited until the battery is full.
- Connect equipment
Plug computers, network equipment and storage into the 4 battery-backup outlets. Use the 4 surge-only outlets for printers, scanners and accessories that do not need to stay on during an outage.
- Set up automatic shutdown
Connect the USB cable from the UPS to the computer and install the manufacturer's power-management software (or use the operating system's built-in UPS support) so it shuts down gracefully before the battery runs out. Connect the Ethernet management port and configure its IP address so servers and administrators can monitor the UPS.
- Run a self-test
Once the battery is charged, start a self-test (usually by holding the power or test button, or from the software) to confirm that the UPS transfers to battery correctly.
Using your UPS
How this UPS protects your equipment
As a line-interactive UPS, it corrects moderate over- and under-voltage with an automatic voltage regulator (AVR) without using the battery, and switches to battery within a few milliseconds during an outage or a severe disturbance. Its default operating mode is classified as VI (voltage independent).
Battery runtime
According to the certification record, the internal battery provides about 3 minutes at full rated load (800 W) and about 11 minutes at half load (400 W). Runtime is not linear — halving the load usually more than doubles it — and it falls as the battery ages or gets warm. Use the runtime to ride through short outages and to shut systems down cleanly during longer ones.
Monitoring and alerts
The UPS provides USB and Ethernet communication. Configure email or SNMP alerts for on-battery, low-battery, overload and replace-battery events.
Alarms and everyday use
- An intermittent beep usually means the UPS is running on battery. Save your work; if the outage continues, shut down connected equipment before the low-battery alarm.
- A continuous tone or overload indicator means the connected load is too high. Unplug non-essential devices from the battery outlets.
- Leave the UPS switched on and plugged in at all times so the battery stays charged.
- If the UPS switches to battery frequently on a generator or in an area with unstable voltage, adjust its input sensitivity setting as described in the manual.
Care and maintenance
| When | What to do |
|---|---|
| Monthly | Check the front-panel status or software for alarms, confirm the load percentage, and make sure vents are clear of dust and obstructions. |
| Every 6 months | Run a self-test (or confirm the automatic self-test passed). Where supported, perform a runtime calibration during a maintenance window, as it discharges the battery. |
| Every 3–5 years | Replace VRLA batteries. Typical life is 3–5 years at 77 °F (25 °C); roughly every 15 °F (8 °C) above that can cut battery life in half. |
| Annually | Check for firmware and software updates and confirm that automatic shutdown still works by running a controlled test. |
Troubleshooting
Use the front-panel indicators, display messages and event log to narrow down problems. For specific alarm codes, consult the manufacturer's manual or support line.
| Problem | Possible cause | What to try |
|---|---|---|
| UPS will not turn on | Battery disconnected or deeply discharged; input breaker or fuse open; no utility power. | Check the battery connection, verify the outlet or input breaker, and let the UPS charge for several hours before trying again. |
| Beeps and runs on battery with power present | Input voltage or frequency outside limits; loose input plug; generator power. | Check the input connection, try a different circuit, and adjust input sensitivity if the manual permits. |
| Overload alarm | Connected load above the rating; high inrush device on battery outlets. | Reduce the load below 800 W and move printers or heaters off the UPS. |
| Short runtime or self-test failure | Aged or hot battery; battery not fully charged. | Charge fully and retest; replace the battery if runtime remains well below the rated figures. |
| Replace-battery indicator on | Battery at end of life. | Order the specified replacement battery and replace it as described in the manual (or by service for larger units). |
| Site wiring fault indicator | Missing ground or reversed hot/neutral in the building wiring. | Have a qualified electrician inspect the outlet and wiring before connecting equipment. |
| Computer does not shut down automatically | Communication cable not connected; software not installed or not configured. | Connect the USB or serial cable (or configure the network card), install the management software, and test with a simulated outage. |
Energy use and running costs
A UPS uses energy as conversion and charging losses on top of what your equipment consumes. The CyberPower CST135UC2 has an ENERGY STAR weighted efficiency of 98.7%. The table estimates its losses if it supports a steady load 24 hours a day, 365 days a year, at $0.17 per kWh.
| Load | Efficiency | Power lost | Losses per year | Cost per year |
|---|---|---|---|---|
| 25% (200 W) | 98.1% | 3.87 W | 34 kWh | $5.77 |
| 50% (400 W) | 98.7% | 5.27 W | 46 kWh | $7.85 |
| 75% (600 W) | 98.7% | 7.9 W | 69 kWh | $11.77 |
| 100% (800 W) | 98.7% | 10.5 W | 92 kWh | $15.69 |
Even with nothing connected, the UPS draws about 3.38 W to keep its electronics and battery charger running — around 30 kWh ($5.03) a year.
Loading a UPS very lightly lowers its efficiency, so choosing a unit sized reasonably close to your actual load keeps losses down.
Frequently asked questions
How much equipment can the CyberPower CST135UC2 power?
It is rated at 800 W (1,200 VA). Keep the connected load below that — ideally under about 640 W — to allow for surges and battery aging.
How long will the CyberPower CST135UC2 run on battery?
The certification record lists 3 minutes at full load and 11 minutes at half load. Lighter loads run longer; older or warm batteries run shorter.
What type of UPS is the CyberPower CST135UC2?
It uses a line-interactive topology and defaults to VI (voltage independent) operation. Line-interactive designs regulate voltage without using the battery and suit servers, network gear and workstations.
How efficient is the CyberPower CST135UC2?
Its ENERGY STAR weighted efficiency is 98.7%. At half load (400 W) it is 98.7% efficient, losing about 5.27 W — roughly $7.85 a year if run continuously at $0.17/kWh.
How many outlets does the CyberPower CST135UC2 have?
It has 8 outlets, 4 of which provide battery backup and surge protection; the other 4 are surge-protected only.
What battery does the CyberPower CST135UC2 use?
It uses a valve-regulated lead-acid (VRLA) battery (internal). The certification record lists a 3-year battery warranty.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified ups battery backups dataset published by the U.S. Environmental Protection Agency (record certified June 7, 2021), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with CyberPower. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact CyberPower or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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