We were running the old atomic clock on a cart in the MSR, it was being powered by a small UPS unit. Around 13:30 PDT two batteries in the UPS unit failed and produced a very strong odor. Gerardo and Fil quickly discovered the problem and removed the unit from the premises (good catch). The lead-acid batteries are swollen but did not break.
We are running with opened doors (its 5degF outside, -14C) and fans to remove the odor.
"the big stink" seems to have dissipated somewhat. We have closed the doors and now there is just a lingering aroma.