How long will a laptop run w/o cmos battery

['putertutor]

I picked up a laptop today, customer complained of seeing a "cmos message" on power up. Said could get past it (not sure how), and his machine would run like normal after windows came up.

He powered up the unit and there was a message with two options. F10 to reset bios, F1 to enter BIOS options. He then showed me (he was very insistent on completing his demo) how he hit f!, which took him into BIOS and then exited without saving and voila! Windows continued to boot normally.

Later that day I opened it up and found the cmos battery cable was not plugged in, so i plugged it in and yada, yada, yada, he has his laptop back. But I am curious, how long can you run a laptop without a cmos battery? I was under the impression this was short term to say the least, but he said he was putting up with this for at least a week, maybe 10-11 days. Not being incredibly familiar with the power requirements of bios, I actually thought the battery was required or no boot, I'm no sure how this happened. I humbly beg the insight of my fellow nibblers...

[ComputerRepairTech]

How long can your alarm clock last without the 9v battery while its plugged into the wall?

Edit: ok perhaps not a perfect example but was the best I could think of at the time. So without the battery soon as power is lost to the board your settings will be lost. If you use default settings in the bios the only real problem is typically time/date and an annoying message when you first boot the system.

[DanF]

A car battery would be a better example.

[Trusted IT Solutions]

Originally Posted by DanF

A car battery would be a better example.

Car stereo....................

[PCS]

I think ComputerRepairTech's example was right, as long as it's running it will keep the right time but as soon as it is turned off / loses power it will go back to 1989 as a reset alarm will go to 12:00

Never tested but i think as soon as you disconnect a car battery, the engine dies?

will try @ my next service interval

[jbartlett323]

Originally Posted by PCS

I think ComputerRepairTech's example was right, as long as it's running it will keep the right time but as soon as it is turned off / loses power it will go back to 1989 as a reset alarm will go to 12:00

Never tested but i think as soon as you disconnect a car battery, the engine dies?

will try @ my next service interval

actually, a car with a good alternator should keep right on running! This is actually how you would test you alternator!
(Disclaimer: some newer cars ECM's dont like this too much...)

[andcorptech]

I have actually come accross a notebook that would not boot without a working cmos battery. It would hang on boot for whatever reason. From memory it was an old IBM thinkpad but would have to look back in files for exact model. I ordered a CMOS battery for it ( was a non standard) and once replaced all worked fine