If you get the following error when booting your SGI Indigo, it’s means you have a dead battery in it.

Initializing tod clock.
setting secs=0 min=0 hour=0 day=1 month=1 year=0
Can't set tod clock.

On R3000 systems the battery is placed in a socket, but on R4000 systems it’s soldered to the CPU board.

Remove the CPU Board

Locate the battery

Desolder the battery

Ready for new battery!

The replacement battery is called TL-5186, and is still fairly widespread in various internet battery shops, so it should be quite easy locating one. (I bought mine at MDS Battery.)

For further reading, please refer to the Indigo Battery FAQ.