Any device that exceeds UPS power rating (wattage) during regular operation or at startup should NOT be connected to the UPS. In general, the devices with internal motors or compressors should not be connected to UPS, which are also known as inductive loads, such as: laser printers, copiers, paper shredders, water pumps, air compressors, vacuum cleaners.

Make sure that the connected devices are plugged into "Backup" outlets of UPS. If plugged into "Surge Only" outlets, UPS won't provide backup power to the connected devices and thus and the connected devices will not get power supply during power outage.

For safety concerns, it's not recommended. It can lead to overload problem when too many devices are connected. If it's inevitable, please make sure the total power consumption of all connected devices does not exceed the UPS power rating (wattage).

It's recommended to charge the UPS for at least 8 hours before use, even though UPS can still be used without power charge before use. Otherwise, the UPS may not be able to provide sufficient backup power for the connected devices if the UPS isn't fully charged when the power outage happens.

If the connected devices to be protected are on all the time, then the UPS should stay on at all time, too.
If not, you can choose to turn it off or not. UPS consumes very little power in idle mode.

Generally speaking, it is not recommended. If it is inevitable to use UPS in this way, make sure the fan or vents are unblocked so that the UPS has enough ventilation.

Since UPS has function of Off-mode Charging, as long as the input utility power is constantly available, UPS will charge the battery whether it's on or not.

The "Backup" outlets provide connected devices lightning surge protection and stable voltage, as well as battery backup power during power outage. The "Surge Only" outlets can only provide connected devices lightning surge protection, but not battery backup power during power outage. For critical devices such as computers, monitors and data storage devices, please plug into "Backup" outlets. Other less important devices like speakers, scanners and fax machines, please plug into "Surge Only" outlets.

The buzzer beeps to remind users that the battery power is discharged. The beeping can be muted manually if users find it disturbing. However, the buzzer will beep fast and compact continuously when the UPS is in low battery or having fault situation and it cannot be muted.

Autonomy refers to the battery backup time at a certain loading level. UPS batteries of different sizes can support loads from minutes to hours, but at high load levels the cost of large batteries sometimes means that diesel generators should be considered. Increasing "autonomy" can be done by adding additional battery strings in parallel, but it is important to take the charging capacity of the UPS system into account.

Critical loads are equipment that must keep running during power outages, for example, a data centre’s servers or life support equipment in a hospital.
That is to say, non-critical (or non-essential) loads like printers, office lighting, and desk fans are not essential to the organization’s operation, which means they can be off during power outages.

An uninterrupted power supply (UPS) can protect loads from the mains power problems, like spikes, brownouts, fluctuations. It serves three basic functions:
1) Avoids data loss and damage. In fact, without a UPS, data stored on devices subject to sudden shutdown can be damaged or completely lost. 
2) Ensures the availability of networks and other applications while avoiding being shut down.

AVR also called an Automatic Voltage Stabilizer (AVS) or Voltage Regulator. AVR supplies stable power voltage to a load. It is a feature of Line Interactive UPS and provides protection from power fluctuation problem.
When the input power voltage is too low, the AVR will boost (step-up) the output voltage. On the opposite, when the input power voltage is too high, the AVR brings the voltage down to a safe range (also known as buck or step-down).  

The fans in UPS are used to keep internal electronic components cool so that they can operate safely. The fans can keep essential components cool. In general, the bigger the UPS is, the more/bigger fans will be used. If the internal fans don’t work properly, these components will run at much higher temperature, which can lead to deterioration or damage.
Environmental factors in workplace like dust can also lead to overheat problems and further affect the life of fans and UPS itself. So it is important for UPS to proceed cleaning maintenance regularly.

A brownout is also called as "sag", is a drop in voltage in an electrical power supply system. When a brownout happens, the voltage will drop from normal level to a lower voltage and then come back. Basically UPS can handle a drop in the nominal voltage if it is within regulation range; however, if the voltage falls outside the range, then the battery will take over without any disturbance to the load. Brownouts can be noticed from lights flickering or dimming or during heavy load periods or severe weather conditions. Brownouts can actually damage IT loads, sometimes even worse than blackouts. In a blackout, the power simply goes off, while in a brownout the device still gets low level power, and some devices will malfunction rather than total shutdown.

A blackout is a total loss of power. Blackouts probably cause no damage to devices if they are in idle. However, if devices are in operation when power goes out, they will most likely suffer from the loss of power, along with spikes when power comes back on. All in all, blackouts can potentially cause great damage to devices.

The product of UPS can protect your data and keep you connected during brownout or blackouts.