ALERT: Nice 218-2 (DAY-DATE) I think this is the true "hack" movement.
REMOVE that battery ASAP. There looks to be leakage around the negative seal. The battery cavity will need to be cleaned out. Ultrasonically is best. Then a fresh #344 battery installed Positive side down. Humming does not mean working... push stem in watch second hand and minute-hour hands for proper rotation. When I see potential problems, I report them. Crystal is fogged needs replacement or pro polishing. I really don't know why Bulova case insides had instructions. In the day the old Mercury 218 Cells were used and sold by Bulova. Unscrewing the battery retainer and battery replacement required a Jeweler / watchmaker. I find that holds true today. Any dust, I mean a tiny invisible to the naked eye particle gets into your tuning forks, your watch will stop.
Nice example 218 Day Date Stainless N-6
John V. "Time & Again"
Specializing in Vintage Accutron Service and Complete Restorations