i have a APC UPS........
suddenly today the redlight got lit up
and it means that the battery is near to its end....
don't have any idea about UPS's battery sytem
my question is what will happen is battery expires
wud it totally stop my computer from running or
wud it only effect the PC during the power outage
It only affects the PC during an outage, but it will probably beep incessantly until you get it repaired. UPS units usually have to have the battery replaced about every 3 or 4 years. Unfortunately, that's not a cheap thing to replace... where I used to work, I was the one that took them to the shop to be replaced... and the battery usually ran between $60 and $80 USD.
And for that price, you might as well just replace the whole unit. That way you get a new warranty too. :D