Nylon-tipped tweezers for handling watch batteries. 

Why? - two reasons. 

Firstly, if you use metal tweezers and accidentally touch both sides of the battery, you will "short" it.  It will still work, but only for a a week or two, then the customer will complain.

Secondly, getting greasy finger marks on a battery shortens its life. If the battery is for a scale or a torch, this won't be noticeable, but if it's meant to last for two or three years in a watch and only last a few months...the customer will complain.