The invention provides an assembled battery and a charging system, allowing reliably informing a charger of the information necessary for the safe charging of a secondary battery and performing the safe charging, and enabling an old-type charger which controls the charging by detecting the battery temperature to perform the safe charging. According to the voltage and the temperature of terminals of the secondary battery, four charging conditions for the safe charging of the secondary battery is distinguished, and one of control voltages at four levels with different voltage levels is selected and outputted to the charger. Specially, according to the voltage and the temperature of the terminals of the secondary battery, one of four charging conditions predetermined according to the combination of voltage regions and temperature regions is selected, wherein the voltage regions are formed by dividing the terminal voltage region of the secondary battery to three levels in advance, and the temperature regions are formed by dividing the chargeable temperature region of the secondary battery to two levels in advance.