Given the spectrum of wristwatches that flow through Hong Kong, I’m amazed at how difficult it is to locate (based on this thread) a source for watch batteries.
In the states, I would’ve found the watch (and hearing aid) battery display at Home Depot, Menards, Best Buy, Walmart, Walgreens. If it were a tough search, I’d even hit up my Jewelry Tools Supplier as they carry the full line of Renata cells.
SR48 might be how it’s listed by ONE manufacturer, but that same cell may carry an altogether different model number.
The Renata chart shows this cell to be the equivalent of their 309: Silver Oxide 1.55v. The 393 battery is another likely compatible contender.
Even the SIDEWALK-camping watch repair uncles throughout HK ought to carry the 309 or 393 cell.