|On old 486 boards, they usually used a Dallas battery chip which was soldered to the motherboard and was not replaceable. Some boards used several watch type batteries welded in series. Some higher end boards had a connector which you could connect an external battery pack to.|
Look for a black chip about one inch long, 3/8ths inch tall and 3/8ths inch wide and says Dallas on the top, that will be your CMOS/BIOS battery. If you don't see that, look for a stack of watch size batteries stacked together. Now look for a two pin connector near it. If you have one it will be labeled for an external battery.