Vintage Synth Repair

Greetings,

When I power up my SQ-80, I get a low battery warning.  Before I take 
care of that, I want to save what's in memory to floppy.  Not having any 
manual (the SQ-80 was a gift with no docs), it was still easy to access 
the floppy drive.  But I get an error message no matter what function I 
select:
No disk in drive
press any button to continue
The light on the drive lights up but no whirring sound of a spinning 
disk is heard.

So I went on-line and found user and service manuals.  I learned that 
although the disk is supposed to be DSDD, HD will work, too.  There was 
nothing about how to diagnose the disk drive.  I see nothing regarding 
replacing the battery, either.  If someone can point me to a resource 
that has the info I need, I'd appreciate it.

In terms of playing and programming sounds, the keyboard is working fine.

Cheers,

Bill