Bob Shuman wrote:
Not clear what "backup" battery you are referring to here that is
"working
fine", but I'd strongly suspect the on (mother) board backup battery
is weak
or dead. Replace it with a fresh one, reset your BIOS, and then
report
back. Or, tell us how you know that the on board backup battery is
known
good.

Bob


Thanks Bob. The ThinkPad's large yellow lithium "backup battery" is 3
volts and I've also tried using a different battery with the same
result. I think this is the only on board battery. One times in ten it
*can* be powered up with the backup installed, in which case the
computer works fine, so I don't think it's a terminal system board
fault.