The manuals for the Pfaff 1475 and 7570 state: 
replacement batteries are 2 Mignon cells, 1.5V, type LR 6. 
Only use leak-proof batteries!

Use Duracell or Energizer alkaline AA batteries.  A good 
quality battery is all you need.

You should check your batteries yearly.  If the batteries 
start to leak or corrode, it isn't good for your machine.

Even if you have your machine serviced every year...
don't think the techs will automatically check.  
Some may but many don't.