To orient groups of products to be packaged in a plastic film the groups are wrapped in lengths of film and fed between two series of opposite conveyor belts. The monitoring circuit is operable for monitoring a battery pack that includes a plurality of cells, and for checking an unbalanced condition of the battery pack in each cycle of a plurality of cycles. The slot has a releasable locking means therein, and the tab has a connection means, which is releasably engaged by locking means.