T 23, how long memory without Cmos battery?

Hi group,

A friend has had some problems with his Cmos battery, which I
had fixed for him. So we decided to swap batteries for a week.

I took mine out and went to see him. We swopped. When I came
back home some 3 hours had passed. To my surprise, when I booted
up, I did not need to set Time and date, and was not thrown into
the Bios setup at all.

I thought that any more than a few minutes of having the Cmos
battery removed would have the Thinkpad forget those settings.

The Thinkpad was obviously switched off. Its power brick was plugged
in but the main battery removed.

T 23.


Lars
Stockholm

The easiest test to do is to remove AC power from the system and then
remove the battery. Wait 5-10 min then plug in the system and boot it
up. If you get thrown into the BIOS; then the obvious conclusion is that
there is a "trickle" circuit when AC is available that supplies the same
power that the CMOS battery does.

Phil Sherman


Lars wrote:
> Hi group,
>
> A friend has had some problems with his Cmos battery, which I
> had fixed for him. So we decided to swap batteries for a week.
>
> I took mine out and went to see him. We swopped. When I came
> back home some 3 hours had passed. To my surprise, when I booted
> up, I did not need to set Time and date, and was not thrown into
> the Bios setup at all.
>
> I thought that any more than a few minutes of having the Cmos
> battery removed would have the Thinkpad forget those settings.
>
> The Thinkpad was obviously switched off. Its power brick was plugged
> in but the main battery removed.
>
> T 23.
>
>
> Lars
> Stockholm

Most computers, laptop or otherwise, have the trickle circuit to power the CMOS,
thereby prolonging CMOS battery life... Ben Myers

On Wed, 28 Mar 2007 17:40:49 -0400, Phil Sherman <> wrote:

>The easiest test to do is to remove AC power from the system and then
>remove the battery. Wait 5-10 min then plug in the system and boot it
>up. If you get thrown into the BIOS; then the obvious conclusion is that
>there is a "trickle" circuit when AC is available that supplies the same
>power that the CMOS battery does.
>
>Phil Sherman
>
>
>Lars wrote:
>> Hi group,
>>
>> A friend has had some problems with his Cmos battery, which I
>> had fixed for him. So we decided to swap batteries for a week.
>>
>> I took mine out and went to see him. We swopped. When I came
>> back home some 3 hours had passed. To my surprise, when I booted
>> up, I did not need to set Time and date, and was not thrown into
>> the Bios setup at all.
>>
>> I thought that any more than a few minutes of having the Cmos
>> battery removed would have the Thinkpad forget those settings.
>>
>> The Thinkpad was obviously switched off. Its power brick was plugged
>> in but the main battery removed.
>>
>> T 23.
>>
>>
>> Lars
>> Stockholm

Another tip...

After you have removed the Main Battery, A/C adapter and CMOS battery, hold
down the power switch for 30 seconds.

This will bleed off any left-over internal voltage that may be lying around
in caps or whatever else.

This is also how you reset the Power Manager on most ThinkPads (except you
don't have to remove the CMOS) starting with the T20. If I remember
correctly, the TP600 series may have had a pinhole near the power switch for
this (I could be wrong. It's been a while since I saw a TP600 )

-Larry

"Phil Sherman" <> wrote in message
news:MGFOh.525$.. .
> The easiest test to do is to remove AC power from the system and then
> remove the battery. Wait 5-10 min then plug in the system and boot it up.
> If you get thrown into the BIOS; then the obvious conclusion is that there
> is a "trickle" circuit when AC is available that supplies the same power
> that the CMOS battery does.
>
> Phil Sherman
>
>
> Lars wrote:
>> Hi group,
>>
>> A friend has had some problems with his Cmos battery, which I had fixed
>> for him. So we decided to swap batteries for a week.
>>
>> I took mine out and went to see him. We swopped. When I came back home
>> some 3 hours had passed. To my surprise, when I booted
>> up, I did not need to set Time and date, and was not thrown into
>> the Bios setup at all.
>>
>> I thought that any more than a few minutes of having the Cmos battery
>> removed would have the Thinkpad forget those settings.
>>
>> The Thinkpad was obviously switched off. Its power brick was plugged
>> in but the main battery removed.
>>
>> T 23.
>>
>>
>> Lars
>> Stockholm

On Thu, 29 Mar 2007 11:47:35 -0400, "Larry" <> wrote:

>After you have removed the Main Battery, A/C adapter and CMOS battery, hold
>down the power switch for 30 seconds.

Thanks guys. I did not need to hold down the power switch. Unplugging
the main power and leaving it out for about ten minutes, with the Cmos
battery out, brought me back to point zero. I never knew about that
trickle thing.

I had replaced my friends Cmos battery with a standard Panasonic 2025.
I use some gooey stuff that is intended for repair of car rear window
heating coils, as a glue. And then put a bit of electric tape around.
I have done this quite a few times for Thinkpads. If it runs OK at
first it usually works for months and years.

His battery had gone quite dead in just a year! There was only 0.3 V
in it now. I replaced it again and now it works fine.

It is quite tricky to plug that battery back in in the T machines!

>This is also how you reset the Power Manager on most ThinkPads (except you
>don't have to remove the CMOS) starting with the T20. If I remember
>correctly, the TP600 series may have had a pinhole near the power switch for
>this (I could be wrong. It's been a while since I saw a TP600 )

It seems you are right. I have never needed to do that, but now on
checking my 600's, one X and one E, I see they both have something
in a hole near the power switch.

Lovely machines, the 600's. I have several, and some of them I keep
running for weeks on end. Never a problem with them!

Lars
Stockholm