Cannot be too safe when you wash your bike

I am particularly careful since I have my Stages power meter installed. If any of the tabs on the battery cover is broken, water may get into the battery casing and causing the CR2032 to drain out quickly. You only need less than 1 ml of water inside to cause that.

Any large sandwich size zip lock bag will work the trick

A less than 10 cent zip lock bag of large sandwich size will do a nice job.