If batteries for emergency-lighting purposes are based on other electrochemical systems, then it results in major problems and low battery reliability. For example, nickel metal hydride batteries can not be used for the floating service. This is caused by charging problems: a trickle charging with the timer is required after a quick discharge. In addition, nickel metal hydride batteries have a narrow temperature range (between 0 and +40°C.) A different electrochemical system is used in lead batteries which should be handled with an outmost care: the battery can be charged only above the freezing point in a temperature range between 0 and +40°C and shall not be placed near spark-generating devices (near switches, fuses, etc.) because a combustible gas is discharged during the battery charging.