Please be careful when doing this procedure. If you use a battery charger, or a spare battery, the potential exists to have a cable shift and short to ground, not a good thing. I have never tried the 9V radio battery, but sounds perfect! I'll try it next time I do a battery removal.
Now for the real safety tip. Always disconnect the negative terminal first. If your wrench grounds while disconnecting, there is no arcing, there is zero potential between ground to ground. If you were working on the positive, it could actually weld to the ground and now you have an electrical fire you can hardly extinguish. When reconnecting, reverse the order and connect the positive first.
Always remove rings, bracelets, and necklaces. My fried almost lost a finger when his wedding band shorted to ground and turned red hot. He still has a circular scar on his ring finger. It's kind of like cutting a section of bark off a tree all the way around!