I have noticed there is a jumper setting for "ext bat" (external battery?) near the battery when it was soldered on the PCB, what is this?

There are usually four layers of copper in a motherboard, the two "middle" ones being reserved for GND and +5v (but i've seen exceptions, and i think that more recent motherboards might have more than four layers). So your battery's negative is connected to the board's GND for sure. Ext_bat is the header for external battery, you can connect there a pack providing 4.5-6v (pins 1 and 4, and i think the jumper on pins 2-3 has to be removed when working with an external battery). If you replace the battery soldered on the motherboard you must use a rechargeable one, whereas the external pack doesn't get recharged.

If I use an external could I use 2 AA battery's or a CR2032 button battery all though that would only be 3 volts and not 3.6 volts would this be good to use or bad? How long would the AA battries or CR2032 battery last for if there good to use?

Sorry I forgot you said "you can connect there a pack providing 4.5-6v" but how long would a few AA battries last? would it be like a CR2032 battery?

I found this page that shows the motherboard layout but there is not much info about the external battery jumper pins I need to know which one is positive and negative the page is:

http://www.rainbow-software.org/manuals/m321.html

the pins are like this:

X X X X - the two middle ones at the moment are closed

I have a 4*AAA battery pack that i'm using with success, and so far only one 486 board refused to boot with it connected - perhaps 6v was too much for it. Cannot tell about CR2032 vs AA(A) longevity, i'd say some quality AAA's should last much longer than a CR2032 based on capacity alone, but maybe their self-discharge rate is also higher, who knows. Anyway, i wouldn't solder another NiCd/NiMH barrel battery that will surely leak and destroy that motherboard in the future. As someone here said (sorry, forgot who/where): "use a external pack, someone will thank you in 20 years" 😁

Based on the pictures you provided, my guess is that pin 1 (towards the edge of the board, and having a square pad on the bottom layer) is the positive, and pin 4 negative. A multimeter would provide the definitive answer - set it on continuity check and see which pin is connected to the board's GND.

Thanks Quicknick the square pin looks to be positive from the continuity check with a multimeter like you said as the square pin is the only one that runs to a diod with the anode side showing it to be positive and the other pin 4 has a continuity with the motherboard power plugs pins 5,6,7,8 that are negative.

one last question, Quicknick said the external battery can use 4.5-6v but can it use 3.6 volts as im looking to use this battery:

https://www.jaycar.com.au/lithium-nipple-aa-3-6v/p/SB1774

its a Lithium type battery but its not rechargable is this good to use?

If you want to know which battery voltages are OK, find the CMOS chip on the motherboard and look up the data sheet for it. It will tell you the input voltage range so as long as your battery fits within this range then you'll be fine. Some of my boards require less than 4V (so 2x AA) while others require at least 5V (so 4x AA) so make sure you get it right to avoid damaging the chip.

I once rebuilt one of those computer battery clocks:

Computer Clock Battery rebuild

You really don't want more than 3 cells in series.

dosgamer wrote:

You really don't want more than 3 cells in series.

That is not always the case, I have a few 386/486 boards that require 6V in order to keep the time, and it does say so in the manual. 4.5V is not enough in those cases.

I suppose it depends on the voltage drop caused by the diodes in series between the ext. battery header and the RTC chip.