Uninterruptible Power Supply (UPS), should it always "ON"?

[dr. d]

So whether leaving it on or off has no effect on the power pack lifespan? I have this habit of turning it off for the weekend or long holiday.

i think, some batteries deteriorate faster if they stay un-charged for long periods, like our car batteries.
if the batteries are fully charged, i think we can unplug them over the weekend.

however, if the neighborhood experiences a lot of power outages, it is a good idea to keep the ups always plugged, to insure the battery is always fully charged when you have to use the appliance plugged into it.

[oj88]

On UPS battery charging:
Most any modern UPS will charge the batteries even if it's switched off. Most will even give off a relay 'click' when you plug them in, signifying that the circuit is active. Yes, I've confirmed this with a lot of APC, TrippLite and many china-branded UPS.

On switching off the UPS:
If the PC or the load connected to it is turned off, it is best practice to turn off the UPS as well. Otherwise, in an event of a blackout, the UPS will transition to backup power even though there's nothing to supply power to, draining the battery unnecessarily.

On adding an AVR:
Most UPS nowadays have basic voltage regulation built-in. This feature may often be called buck/boost. Buck is reducing the output while boost is the opposite. Each step, whether buck or boost, is usually between 10-20V apart. So for a 20V boost for example, if the input voltage gets down to 200V, it will boost the output back to 220V. Many UPS will have multiple buck/boost steps, allowing you to power up your PC even if the input voltage is down to 180V.

If your UPS does not have a built-in voltage regulator, you can put an AVR before the UPS, not after.