Portable Battery Compartment a boxy, Portable battery compartment, that allows you to take your Watch Winders with you on Holidays, so you never have to worry about resetting your watch or winders. The portable battery compartment is compatible with both the Double Watch Winder and the Brick Watch Winder. The Portable battery compartment requires 4 x "D" size batteries. Batteries not included. It is not recommended to use this with more than two winding units.