CMOS Batterys- why do they fail?

  SparkyJack 10 Jun 11
Locked
Answered

I am sure many of us has had to change the CMOS battery in our desktops at some time because 'Time was slowing down'

One of my flock was bemoaning the fact that an ASUS laptop was showing the same symptoms and he was unable to discover how to get at it- *'not with standing carrying out all the obvious searches' *said he

I could not help him either.

It later occurred to me is there a good reason why these items in any computer are not of the rechargeable variety?

  woodchip 10 Jun 11

They run down like all battery's, But Cmos Battery only keeps the BIOS clock on Time. When PC is switched off, unless the mains plug is left switched on, this is for desktops. I would not suggest that a Laptop be left with Mains Adapter turned on all the time. Desktop will run of the small amount of power to the motherboard when it switched of but mains plug at wall socket is left in and switched on. The Cmos Battery will then last much longer

  chub_tor 10 Jun 11
Answer

Once upon a time some desktop PCs had rechargeable batteries, certainly my first Elonex with a 386 processor had one, but at that time the drain on the standby battery was considerably higher than it is today. Extra components were required to make up the charging circuitry and these of course added cost to the system. As the power drain decreased with improved CMOS design and battery technology improved it became more economic to use a simple single button cell requiring replacement every 2 years or so and they have now become the de-facto standard. As any owner of a rechargeable battey will know these don't have an indefinite life anyway and they still have to be replaced after a certain number of charging cycles. So balancing the extra cost of a rechargeable cell plus its added charging circuit against the cost of a simple lithium cell it becomes more ecomomical to use the simple non-rechargeable cell.

  SparkyJack 11 Jun 11

Good old economic logic I guess as club_tor pointed out rules the roost here as any where - Most technology it seems has buried in its complexity a basic fundamental harking back to the dawn of its time

This applies to Homo Sapiens too I under stand.

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