The battery will be connected between pins 1 and 4. Easiest way would be to use a multimeter to determine which one is the ground pin.

Next option is to visually trace the connections. The GND pin will appear to be not connected to anything (but it connects to an internal ground plane of course), while the positive one will usually go to the anode of a diode (or string of diodes).

Which leads us to the third options, trial and error. So far I haven't encountered a board where connecting the external battery in reverse would lead to any damage, it just doesn't work. That's because of the series diode(s).

If someone else doesn't already use this same board and could point you to the proper voltage, some trial and error will be necessary for finding it. I'd suggest starting with 4.5V. There are some boards that hang while POSTing with too high a CMOS voltage (6V), and others that can't keep the settings or the clock doesn't run if the voltage is too low.

Sounds like yours is similar to Need help resurrecting a 486 dumpster find so perhaps you will arrive at the same solution.

quicknick wrote on 2020-08-16, 19:42:

The battery will be connected between pins 1 and 4. Easiest way would be to use a multimeter to determine which one is the ground pin.

If someone else doesn't already use this same board and could point you to the proper voltage, some trial and error will be necessary for finding it. I'd suggest starting with 4.5V. There are some boards that hang while POSTing with too high a CMOS voltage (6V), and others that can't keep the settings or the clock doesn't run if the voltage is too low.

Agree ! On most but not all Pin 1 is + and 4 is - , but not all. And 4.5v (3x AAA or AA) would be the best as most use that, there are a rare few that suggest 6v in their manual (out of my 20+ 286, 386, 486 only 2 use 6v, the rest are 4.5 ext batt)

Soyburger wrote on 2020-08-16, 18:28:

Hello, I recently purchased a BC3486UL motherboard from eBay that had a corroding battery. Needless to say I’ve cleaned it all u […]
Show full quote

Hello, I recently purchased a BC3486UL motherboard from eBay that had a corroding battery. Needless to say I’ve cleaned it all up. The motherboard works great and I’m trying to connect an external battery to the external battery header.

I got the specs from stason.org but the manufacturer is unidentified and it doesn’t have the pinout of the external battery header.

Does anyone know the pinout or what voltage battery I should use. It has 4 pins and pins 2 and 3 were jumpered to use the internal battery

I’m not married to any solution I can do normal AA’s at 3, 4.5 or 6 volts, I can do a 3.6v (that’s what the soldered battery was) I can do 3v coin cell.

Any help would be great, I don’t want to do trial and error and blow something up.

Thanks for any help.

Do you have any photos of the board ?

Sorry for bumping this thread, I got the same mainboard and was wondering if you ever figured out which pins to connect.

Long story short: I think I need to put the jumper on pins 1 and 2, connect pin 3 to the + of a 3V battery (pack) and pin 4 to the - of the battery (pack), right?

Long story:
Pins 2 and 3 are “jumpered”.
As you can see on the picture, the + of the internal battery is going to a 0.69k resistor and then from the resistor to pin 2, which is bridged by a jumper to pin 3 which goes to the collector of transistor Q1.
Pin 1 goes to F1 (lane on the back side), which I assume is a fuse.
Pin 4 is the ground, checked with a multimeter.

I assume that the jumper needs to be put on pins 1 and 2, which connects the internal battery to the fuse, as there is no internal battery, it essentially is an open circuit.