System comprising a power device and only one portable device, wherein the portable device comprises a battery and the power device is configured to wirelessly charge the battery, wherein the power device comprises an antenna configured to emit a magnetic field with a carrier frequency to power the portable device, and wherein the portable device further comprises an antenna, a matching stage, a rectifier stage and a charge stage, and wherein said charge stage is configured to sense and limit the rectified antenna signal and characterized in, that the charge stage comprises a charger IC including an input pin connected to the rectifier stage and an output pin connected to the battery, wherein the antenna of the portable device is configured to be exposed to the magnetic field and connected via the matching stage to the rectifier stage to rectify an antenna signal to provide an input voltage (Ui) at the input pin of the charger IC, and wherein the charger IC being configured to provide a first charge current (Ic) at the output pin to charge the battery for a first period of time as power source with the constant first charge current (Ic), and wherein the portable device comprises a detuning stage to change the resonance frequency of the antenna of the portable device and that the charge stage is built to limit the input voltage (U I) for the charger IC by steering the detuning stage to detune the resonance frequency of the antenna of the portable device away from the carrier frequency of the magnetic field, wherein the power device is built to receive and process a power adjustment information from the only portable device exposed to the magnetic field to increase or to decrease the power of the magnetic field emitted by the antenna of the power device and wherein the charge stage of the portable device is built to generate the power adjustment information for the power device to increase or to decrease the power of the magnetic field to steer the input voltage (U I) of the charger IC in a preferred voltage range, in particular within the voltage range of the technical specification of the charger IC, and wherein the portable device is built to provide a second charge current (Ic) at the output pin of the charge IC to charge the battery for a second period of time as power source with the constant second charge current (Ic) higher than the first charge current (Ic) and to provide enough power for the ramp-up from the first charge current (Ic) to the second charge current (I C) and the charge stage comprises a temperature sensor and is built to send a power adjustment information to the power device to increase the power of the magnetic field and to substantially at the same time detune the antenna for a ramp-up period of time (T R) to avoid that the sensed temperature (T L) reaches a maximum temperature limit. wherein the portable device comprises a battery and the power device is configured to wirelessly charge the battery, wherein the power device comprises an antenna configured to emit a magnetic field with a carrier frequency to power the portable device, and wherein the portable device further comprises an antenna, a matching stage, a rectifier stage and a charge stage, and wherein said charge stage is configured to sense and limit the rectified antenna signal and characterized in, that the charge stage comprises a charger IC including an input pin connected to the rectifier stage and an output pin connected to the battery, wherein the antenna of the portable device is configured to be exposed to the magnetic field and connected via the matching stage to the rectifier stage to rectify an antenna signal to provide an input voltage (Ui) at the input pin of the charger IC, and wherein the charger IC being configured to provide a first charge current (Ic) at the output pin to charge the battery for a first period of time as power source with the constant first charge current (Ic), and wherein the portable device comprises a detuning stage to change the resonance frequency of the antenna of the portable device and that the charge stage is built to limit the input voltage (U I) for the charger IC by steering the detuning stage to detune the resonance frequency of the antenna of the portable device away from the carrier frequency of the magnetic field, wherein the power device is built to receive and process a power adjustment information from the only portable device exposed to the magnetic field to increase or to decrease the power of the magnetic field emitted by the antenna of the power device and wherein the charge stage of the portable device is built to generate the power adjustment information for the power device to increase or to decrease the power of the magnetic field to steer the input voltage (U I) of the charger IC in a preferred voltage range, in particular within the voltage range of the technical specification of the charger IC, and wherein the portable device is built to provide a second charge current (Ic) at the output pin of the charge IC to charge the battery for a second period of time as power source with the constant second charge current (Ic) higher than the first charge current (Ic) and to provide enough power for the ramp-up from the first charge current (Ic) to the second charge current (I C) and the charge stage comprises a temperature sensor and is built to send a power adjustment information to the power device to increase the power of the magnetic field and to substantially at the same time detune the antenna for a ramp-up period of time (T R) to avoid that the sensed temperature (T L) reaches a maximum temperature limit.