The first Silicon Graphics workstation I owned was an SGI Iris Indigo R3000 running IRIX 5.3.
One of the problems I ran into with the Indigo was that one day when I turned on the workstation it reported:
Initializing tod clock. setting secs=0 min=0 hour=0 day=1 month=1 year=0 Can't set tod clock.
This is caused by the on board battery being empty.
The battery in my Iris Indigo R3000 had part number TL-5186 - 3.6V 370 mAh - and was produced by Tadiran. The TL-5186 has been discontinued and was replaced by the TL-4986.
In my case the battery was not soldered onto the motherboard and removing the rubber band that keeps the battery in place was enough to pull out the battery. But before I could reach the battery I had to unscrew a piece of protective transparent plastic - see above photo.
SGI The Netherlands sent me a replacement battery for free (thanks!).
The following one liner reports the serial number of an Iris Indigo R3000:
/usr/etc/netstat -ia | grep 08:00 | sed 's/ *//;s/://g' | head -1 | tr '[a-f]' '[A-F]'