I Have a 1000 va pure sine wave UPS connected to my PC my Router and My switch
at nigh I turn OFF my PC
my question is
which is better for the lifespan of my UPS and the batteries to unplug it from wall at night or just to keep it plugged 24/7 ?
The batteries should be replaced after 3 to 5 years. The number of discharges and amount of discharge impact the lifespan more than anything else. You probably want the router, and WIFI for your phone, etc, to be on at night so I would recommend you just leave the UPS on 24/7. It was designed to be plugged in and on. Just budget to replace the batteries after about 4 years.
Theoretically instead of 24/7, u have it on only 16/7 would save wear/tear, but this is in the category of O.C.D. U never surf while in bed before you fall asleep? Don't u ever wake up in the middle of the night and want to find out last night's score? U don't have, never schedule an update, backup, defrag in the middle of the night? U know that broadband modem, the ISP sends update to it once in a while, and the few times I had problem with them is when I turn it off for an extended amount of time (hours), they don't seem to like it, so if u wanna go through all that trouble, be my guest.
My AC is reliable as in any Western country one can expect and rarely any storm here, but my UPS battery used to die 2 years on the dot it seems, until I scheduled a weekly self-test on the UPS, I believe my current battery is on its 4 years! YMMV.