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View Full Version : Don't forget the battery in your PC/AT!



ChrisCwmbran
August 18th, 2013, 02:27 PM
Just a reminder for those of you who have IBM PC/ATs!

Last week I powered mine up for the first time in a while and the battery burst and leaked. What is more looking inside the machine which was donated to me, a previous battery had clearly leaked and left an unpleasant mess which damaged the RTC chip:

http://www.minuszerodegrees.net/5170/battery/5170_battery.htm

I think I'm going to have to replace the MC146818P chip that has suffered - fortunately a replacement chip isn't too hard to find.

That said it's much easier just to remove the battery when the machine isn't going to be used in a long time, and avoid this problem happening to you!

Now I just need to decide whether to use 4 x AA batteries in a holder or a coin cell. Personally I've never seen a coin cell leak but I know it can do.....

Stone
August 18th, 2013, 02:40 PM
While the coin cell is unlikely to leak the AA setup contains 100 times the capacity of the coin cell and while I have no idea how long a coin cell will last in an AT 100 times longer is nothing to sneeze at -- no pun intended. :-)

ChrisCwmbran
August 19th, 2013, 03:04 AM
I presume this battery is also used for the retention of the hard drive parameters etc.

Can anyone confirm this?

mikey99
August 19th, 2013, 10:53 AM
I've used the 4XAA battery holders on several computers successfully, one an IBM PC/AT .
Its always best to mount the 4XAA holder on the outside of the computer, in case
the batteries start leaking.

They always start leaking eventually. Its just a theory..... but I suspect that alkaline batteries
do not like a slow/constant current draw. They are designed to be used in a device that
is either ON or OFF. They will work in this application, but it seems like they start leaking sooner
and make a bigger mess !

Chuck(G)
August 19th, 2013, 11:10 AM
I've used alkalines without leakage problems and keep the battery holder inside the cases--bit it's always in a plastic bag. You could probably use a better (plastic) container just as well. I've never had a problem with leakage after the original on-bard battery has been removed.

Anyone ever try using silver-oxide batteries? I've never seen one of those leak.

yuhong
August 19th, 2013, 07:51 PM
I am glad the CR2032 button cell batteries rarely leak, as patching high speed traces on a modern motherboard is probably much more difficult.

sergey
August 23rd, 2013, 02:08 PM
A fresh CR2032 gives only 3V, which is way less than original 6V, and the same as MC146818P minimal operating voltage...

So I'd vote for three or four alkaline batteries (either AA or AAA type). RadioShack has nice enclosed battery holders for 4 x AA (http://www.radioshack.com/product/index.jsp?productId=2062253) and 4 x AAA (http://www.radioshack.com/product/index.jsp?productId=2062254) batteries. This will also help in case of potential leak.
By the way I've never seen high quality (Energizer, Duracell) alkaline batteries leak or perform poorly in low current conditions. In fact smoke alarms use lower capacity 9V alkaline batteries, and these batteries last for several years (although battery manufacturers and government will urge you to change batteries once a year :-)).

Chuck(G)
August 23rd, 2013, 03:45 PM
Macs used a 3.6V lithium battery for PRAM--has anyone ever seen a leaky one? Odd that PCs of about the same age seem to experience this.

If you're like me and hate changing the battery in a smoke alarm in the middle of a 10-foot ceiling at 4 AM (where's that cricket?), you spend the $5-7 for one and buy a 9V lithium. They seem to last at least 6-7 years and are very popular with apartment landlords.

yuhong
August 23rd, 2013, 04:05 PM
Macs used a 3.6V lithium battery for PRAM--has anyone ever seen a leaky one? Odd that PCs of about the same age seem to experience this.
I remember visiting 68kmla a lot and yes they do leak.

modem7
August 23rd, 2013, 04:08 PM
I presume this battery is also used for the retention of the hard drive parameters etc.
Can anyone confirm this?
Confirmed.


A fresh CR2032 gives only 3V, which is way less than original 6V, and the same as MC146818P minimal operating voltage...
For an IBM AT, the situation is worse because of two isolation diodes. In combination, those diodes drop about 0.8 volts (as measured by me on several IBM AT motherboards), and so if a battery measuring 3 volts is fitted to an IBM AT, the MC146818P chip gets about 2.2 volts.

vwestlife
August 23rd, 2013, 08:20 PM
I remember visiting 68kmla a lot and yes they do leak.

Yes, Mac PRAM batteries do leak... and/or explode! The worst I've ever seen:


http://www.youtube.com/watch?v=t9fgRF1BrcU

k2x4b524[
August 23rd, 2013, 11:27 PM
those traces looked remarkably intact for the amount of damage, you could also find the values of the capacitor and diode and replace those, but would the corroded chips be salvageable, considering that the mac booted up, i would try and do what i could with that board, i also didn't know you could wash a board with simple green and tap water, i'll have to remember that one..

SpidersWeb
August 24th, 2013, 12:55 AM
A fresh CR2032 gives only 3V, which is way less than original 6V, and the same as MC146818P minimal operating voltage...

So I'd vote for three or four alkaline batteries (either AA or AAA type). RadioShack has nice enclosed battery holders for 4 x AA (http://www.radioshack.com/product/index.jsp?productId=2062253) and 4 x AAA (http://www.radioshack.com/product/index.jsp?productId=2062254) batteries. This will also help in case of potential leak.
By the way I've never seen high quality (Energizer, Duracell) alkaline batteries leak or perform poorly in low current conditions. In fact smoke alarms use lower capacity 9V alkaline batteries, and these batteries last for several years (although battery manufacturers and government will urge you to change batteries once a year :-)).

Generally I use 4xAA holders as well and use an old CDROM audio cable (easy to find) to solder them to. On valuable machines I'll also put the holder in a plastic bag and tie it up as well.
BUT I did see a nifty solution in one machine I pulled, it had a dual CR2032 holder soldered closely to the plug, so it kind of just stood up in mid air and provided the 6V.

geoffm3
August 24th, 2013, 07:06 AM
Yeah, I've seen quite a number of Mac PRAM batteries leak. I went looking through a guy's warehouse full of computers and thought I hit the jackpot when I found a IIfx, only to discover that there was a VERY fuzzy battery inside that had corroded a large (think 2" diameter) section of the motherboard around it.