My MD MkII showed me the ‘Low Battery’ warning message, so I opened it up in line with @ach’s photo guide earlier in this topic. It had the soldered-in battery. After contacting Elektron support, who were very helpful with advice, I chickened out of replacing the battery and its clip myself and opted to send it to Elektron’s US workshop. They gave me copious instructions for the return, which made the process run smoothly.
When the repair was done they charged me for 30 minutes of labour to replace the battery and clip, plus $6 for the parts.