Sensor to detect a mechanical stress on the battery pack

A method for controlling a system having a power tool, at least one battery having at least one energy storage cell, at least one acceleration sensor for detecting at least one acceleration value in an X, Y and Z direction, at least one piezoelectric sensor, a controller, signal transmitter and a measurer for measuring a voltage, the method comprising the steps of:

• determining vibration values acting upon the system by detecting acceleration values within a predetermined range;
• determining a free-fall state of the system by detecting an acceleration value in the X, Y and Z direction being equal to a predetermined range;
• determining an impact of the system by detecting at least one acceleration value in the X, Y and Z direction exceeding a first predetermined threshold value;
• determining a traveling distance between the detecting the acceleration value in the X, Y and Z direction being equal to the predetermined range and the detecting the at least one acceleration value in the X, Y and Z direction exceeding the first predetermined threshold value;
• determining a shock value via the at least one piezoelectric sensor or the at least one acceleration sensor;
• detecting a first and second voltage values of the at least one energy storage cell via the measurer for measuring the voltage;
• and
• sending out a first signal via the signal transmitter if the acceleration values within the predetermined range for determining vibrations exceed the first predetermined threshold value for a first predetermined time period, a determined drop height exceeds a further predetermined threshold value, the determined shock value for determining a shock exceeds a yet further predetermined threshold value or a difference value between the first and second voltage values exceeds a still yet further predetermined threshold value.