Question Acer aspire CMOS battery míster y.

[arajigar]

Hi. Recently I bought a second hand Acer aspire 5920, with its battery totally worn out, and also its CMOS cell battery, I kwow it because data in BIOS was 2007; certainly, not the year we live on. Because of that, I purchased a new battery. The surprise came when, once I charged and inserted the New battery, and after changing date and time into Win7, I turned off the laptop, and then turned on it again Just to test if it'll keep the charge.
All was ok, but...
When I cheched date and time... both were still right!!!
I must say that I have no connection to the Internet, and also the Windows time is disabled in services.
But, what surprised me the most is that date and time into the BIOS also was right, and remained intact even with battery detached!!
What does this mean?, had the cell battery take charge from the mai battery in some manner?, was it re chargeable? I have build severa pcs, changed CMOS batteries, and know that once they're gone, data and time neve return, so this situation is confusing me so much.
Any help Will be appreciated.

 

[Lutfij]

But, what surprised me the most is that date and time into the BIOS also was right, and remained intact even with battery detached!!
If you swapped out the CMOS battery in a matter of seconds, then it's possible that the residual power was what retained the power on the board.

Then again,
I kwow it because data in BIOS was 2007
I think you meant to say the date stamp for the BIOS's creation. Did you see the clock set to 12:00 when you first fired the laptop after purchase? If not, then the CMOS battery was fine to begin with.

 

[arajigar]

Hi. The laptop has its main battery dead. And the cmos cell battery is so hidden that i wasnt able to touch it. 😉 And... No, the data and time was for the laptop, it says 00:00 hrs. January the first of 2007 in the task bar. The data of the build, of course, was 2007 (once I looked to the BIOS when I first turned on the laptop and cheked the BIOS to see if the CMOS battery was ok).

 

[BFG-9000]

It's no mystery, since almost all laptops including yours use a rechargeable Li-Ion CMOS battery. This battery is never actually used unless the main battery disconnects from overdischarge or removal, and its capacity is much lower than a primary coin cell.

Given that all li-ion batteries in consumer items are equipped with protection circuits, your OEM CMOS battery simply disconnected once it dropped to 2.5v to protect itself from overdischarge (since attempting to charge a too-low li-ion afterwards could cause a fire). Attaching a charged main battery to it woke it back up and it accepted a charge.