Is the clock actually running? (ie. it actually advances in time once you set it manually?)
Having the machine plugged into the mains doesn't do anything on the SE/30, because the swtich on the back actually turns off the power supply.
There is no standby voltage coming out to keep the RTC chip alive.
Check if you are getting any voltage on pin 8 of the RTC with the battery in place.
Check if diodes D1 and D2 are good. We're going to make sure the RTC is even powered by the battery first.