In a lead storage battery, multiple electrochemical cells are connected in series to get the maxiumum output.
12 cells each having same e.m.f are connected in series and are kept in a closed box. Some of the cells are wrongly connected. This battery is connected in series with an ammeter and two cells identical with the others. The current is 3A when the cells and the battery support each other and 2A when the cells and the battery oppose each other. The number of cells in the battery that are wrongly connected is