Sun dead battery / unresponsive openboot

[Jules Richardson]

The PROM battery appears to have died in my Sun U1 (Ethernet address and 
host ID all ff's etc.).

I can hack a new battery into it at some point - but can anyone confirm 
whether the openboot environment should be responsive even while the 
battery is hosed? Via a serial console, I can send a break and get an OK 
prompt back, but then it appears to go unresponsive and won't accept 
commands (no key presses aren't echoed back to the screen).

Using the same terminal emulator / cabling is fine with my other Sun (a 
U2), so I'm reasonably confident that the environment is OK, and that the 
problem is local to the U1 machine.

cheers

Jules