Date registered: May 2005
Vehicle: '07 GL320CDI
Mentioned: 0 Post(s)
Quoted: 2 Post(s)
I frankly don't worry much about battery disconnecting.
The key is, of course, to be careful.
For DIY, it's your car, so you pay. Professionals need to be careful, as they shouldn't be able to charge for their mistakes.
I'd certainly never worry about this working on spark plugs, coils, etc. If these things retained charges, the engine would still be running. Certainly changed plugs/wires and CPS on an M112 with no worries.