Got this battery operated ultrasonic cleaner from AliExpress for US$3.60 shipped and it’s a godsend!
Used it to clean my vintage watch bracelets. 40/50 years of gunk removed in 30 minutes (3 x 10min sessions) with a quick scrub with a toothbrush in clean water between each session. It’s small and fits one bracelet at a time.
Remember only to use this on the bracelets and not put your whole watch in!