A device for contolling the charging of rechargeable batteries comprises two temperature sensors deposited on a flexible thin thermally and electrically insulating sheet. The thin sheet is disposed around the rechargeable battery so that one of the sensors determines the temperature of the battery and the other sensor determines the ambient temperature. A charge stopping device stops the charging of the battery when the difference between the temperatures determined by the two sensors has reached a predetermined value. The sensors consist of resistors applied by silk screen printing and disposed in a Wheatstone bridge arrangement.