i'll have a trip for about 3 months. since no one home, just for safety, i decide to unplug all the electrical devices except the telephones and the fridge. so i wonder how long the battery cell on the mobo can last without power? and if the battery runs outta power, will my cmos setting reset?

CMOS battery has a design life of 5 years. Some last twice that. Some not a year. I wouldn't worry about it. If the battery were to go dead it won't harm anything. There is a good chance other than the time you may be using the default settings anyway.

I have been messing about with PCs now, both my own and other peoples, for nearly twenty years and in all that time I have only ever had to replace a CMOS battery twice.

5 years plus is not uncommon so in reality you can say the CMOS battery will last the life of the PC.

BTW: Whether power is allied or not makes no difference. The battery in a modern PC is not rechargeable and rely entirely on power put there during manufacture.

Stuart

I normally use power strips to remove all power from computers to save energy. Since the cmos battery doesn't recharge when ac power is on it basically is always un-powered. I have never had a battery go bad.

You don't need the phone plugged in either.

Matter of fact you could get rid of your ice cubes and turn off the fridge. Leave the door open a bit to prevent yuck. (might have to clean it first)

I read it wrong and answer it wrong too. So get off my case you peanut.

I agree with removing the computer from any wall connections when leaving for that long.