Patent Publication Number: US-2021175727-A1

Title: Mobile phone cover comprising two or more charging stations for rechargeable instruments

Description:
TECHNICAL FIELD 
     This disclosure relates to a mobile phone cover comprising a mobile phone holder and two or more charging stations for receiving and retaining rechargeable instruments. It further relates to a medical system comprising N implantable medical devices (IMD), a mobile phone cover, and M rechargeable instruments, wherein M≥N≥2, a rechargeable instrument being configured for powering wirelessly an implantable medical device (IMD). 
     BACKGROUND ART 
     Neurostimulation systems comprising implantable neurostimulation leads are used to treat chronic pain. Conventional implantable spinal cord stimulation leads are designed for placement in the spinal canal as part of a spinal cord stimulation system, and for the therapeutic purpose of treating various forms of chronic back and extremity pain. 
     A neurostimulation system for the purpose of treating chronic headaches is known from WO2017/120357A1. The system includes N implantable pulse generators (IPGs) from which multiple stimulating leads may extend sufficiently to allow for adequate stimulation over multiple regions of the head and an external charge transfer system. One external charge transfer system (ECTS) is configured to charge and to communicate with the N IPGs via N series-connected charge transfer coils. Each of the receive coils of an IPG is tuned to the resonant frequency of the respective charge transfer coil. By sending forward telemetry commands instructing a selected IPG to communicate back telemetry data to the ECTS, the non-selected IPG will forego attempted back telemetry during such times. 
     By using an external charge transfer system outside a dermis layer, the degree of access to the controller is greatly increased, and in some cases, the functionality that needs to be implanted may be reduced in some cases. However, the system may only be operated optimally if the external charge transfer system is correctly configured and fully operational. In addition, when using external units, it may not be possible to operate an implant correctly if the external unit is not present or it is malfunctioning. In some cases, it may not be possible to operate an implant at all with a missing or defective external unit. 
     SUMMARY OF INVENTION 
     It is an objective of the present technology to provide a portable charging device for rechargeable instruments that increases the chance that operable instruments will be available to a user. 
     In many applications where rechargeable instruments are used, common problems including the user forgetting to recharge the instruments and/or the user having too little time to fully recharge the instruments. Especially where the rechargeable instruments are used for a personalized application, such as a personalised therapeutic, stimulation or medical use, users become more reliant and dependent on the correct operation of these instruments, resulting in a severe inconvenience if they are not sufficiently charged. These issues are particularly prominent when the battery lifetime of the rechargeable instruments is less than a day, and require intermediate charging. Carrying specific charging means daily is a burden and may not be consequently done by the user, leading to major discomfort when the instruments run out of power. 
     By providing a portable charging device in a mobile phone case, there is a reduced risk that an instrument will not work properly or be inoperable. There may also be lower chance that the user will forget to take the rechargeable instruments when they are travelling and/or away from home. 
     Preferred dimensions for the mobile phone cover are those suitable for transport in a small bag, and most preferably pocket-sized. 
     Smaller dimensions should preferably be used, as this may increase portability and may increase the likelihood that the user will use the cover regularly, preferably every day. 
     The mobile phone cover described herein is highly configurable—differently dimensioned covers may be provided for one or more specific type of phone, or a more universal mobile phone cover may be provided to receive and retain a wide range of mobile phones. 
     In a further aspect, the mobile phone cover may be modified to provide inconspicuous and unobtrusive storage and charging. In particular, when the rechargeable instruments are configured for one or more therapeutic, stimulation and/or medical uses, the user may not wish others to be aware that they have a condition which requires treatment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, properties and advantages will be explained hereinafter based on the following description with reference to the drawings, wherein like reference numerals denote like or comparable parts, and in which: 
         FIG. 1  shows schematically the components of a neurostimulation system; 
         FIG. 2  shows a block diagram of the EPTD; 
         FIG. 3  shows a block diagram of the IMD; 
         FIG. 4  shows a block diagram of a charging circuit; 
         FIG. 5  and  FIG. 6  show examples of nerves that may be stimulated using a suitably configured neurostimulation system; 
         FIG. 7  shows further examples of nerves that may be stimulated using a suitably configured neurostimulation system; 
         FIG. 8  schematically depicts a charging system; 
         FIG. 9 ,  FIG. 10  and  FIG. 11  schematically depict further charging circuits comprised in a charging device; 
         FIG. 12  depicts schematically a mobile phone cover with discreet storage of one or more rechargeable instruments; and 
         FIG. 13  depicts schematically a further mobile phone cover with discreet storage of one or more rechargeable instruments. 
         FIG. 14  depicts a portion of a further embodiment of a mobile phone cover schematically after the mobile phone has been placed in a holder 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  shows schematically the components of a neurostimulation system according to the present subject technology and  FIG. 8  schematically depicts an example of a charging system comprised in a mobile device cover. The neurostimulation system is designed for the treatment of chronic headaches. It incorporates multiple elements and features that consider the unique anatomic, physiologic, and other related challenges of treating pain with implantable neurostimulation, thereby greatly improving on therapeutic response, patient safety, medical risk, and medical costs, thereby providing an improved overall patient satisfaction. 
     The neurostimulation system comprises four different components: an implantable medical device (IMD)  102 , a rechargeable instrument  104 , such as an external power transfer device (EPTD)  104 , a charging device  106 , and a mobile phone  108 .  FIG. 1  shows two IMDs  102 ; an Occipital Nerve Stimulation (ONS) implant and a Supra-Orbital Nerve Stimulation (SONS) implant. The ONS implant is implanted underneath the skin of the back of the head. The ONS implant stimulates the peripheral nerves using mild electrical pulses. This treatment is used to lower the intensity and frequency of headache attacks. The SONS implant is placed underneath the skin of the forehead and during stimulation an electrical current is applied to the supraorbital nerves, a branch of the frontal nerve. 
     The EPTD  104  powers wirelessly the IMD  102  and it may be mechanically coupled to the IMD by means of magnetic forces. In an embodiment, the IMD comprises an internal magnet and the EPTD comprises an external magnet. In the context of the present description the term “internal” means in the head underneath the skin and the term “external” means out of the head. In another embodiment, one of the IMD and EPTD comprises a magnet and the other comprises a ferromagnetic material. In an embodiment the EPTD functions also as external pulse generator for supplying via the IMD electrical current to the nerves. 
     The charging device  106  is configured to charge an energy storage, such as one or more rechargeable batteries, comprised in the rechargeable instrument  104 , such as in an EPTD. The charging device  106  is further configured and arranged to be portable—in other words, it can be carried. Optionally, the charging device  106  may be further configured and arranged to exchange data with the rechargeable instrument  104 . The charging device  106  comprises two or more charging stations  110 , each configured and arranged for receiving and retaining a rechargeable instrument  104 —in this example, an EPTD  104 . n the embodiment shown in  FIG. 1 , the charging device  106  comprises four charging stations  110 . In the schematic depiction of  FIG. 8 , two charging stations  110  are shown. 
     The fourth component of the system is a mobile device  108 . The mobile device  108  provides a user interface to monitor and set the parameters of the EPTD and IMD and to review the applied therapy. In  FIG. 1  the mobile device  108  is a mobile phone. However, the mobile device can be any device providing a user interface and display enabling a user to control and monitor operating parameters of the EPTD and IMD, such as a tablet computer. Additionally or alternatively, the mobile device may provide a user interface and display enabling a user to control and monitor charging parameters of the EPTD and IMD. 
     Although the phrase “mobile phone” is used, this should be understood also comprising devices which provide a limited (or even no) traditional telephone functionality, such as voice calling, but provide one or means of communicating, such as with messaging apps. In general, “mobile phone” should be interpreted as a portable personal communications device. 
     In  FIG. 1  and  FIG. 8 , the charging device  106  is comprised in a mobile device cover, more specifically a mobile phone cover. The mobile phone cover comprises a holder  120  for receiving and retaining the mobile phone  108 . 
     A mobile phone cover may be made using one or more suitable materials, such as a fabric, a natural material, a plastic and/or a polymer. In the context of this disclosure, a cover for a mobile phone is typically configured and arranged to protect and/or conceal a portion of the external surface (or face) of the mobile phone  108 , such as the screen side or the back. Mobile phone covers are also known which protect and/or conceal portions of more than one external surface (or face)—for example, a cover may conceal and/or protect both the screen and the back, as well as one or more sides. 
     Cases for a mobile phone are also known—traditionally a case is understood to enclose the mobile phone, but some covers also enclose the mobile phone. So, in the context of this disclosure case and cover should be considered as synonymous. 
     The holder  120  is configured and arranged to receive and retain the mobile phone  108 . For example, using one or more magnets, one or more mechanical retainers, one or more protrusions, one or more recesses, one or more fasteners, one or more openings, one or more resilient elements, one or more elastic elements, one or more clamps, one or more hooks, one or more threaded elements, one or more pins, one or more adhesive elements, one or more coatings, and any combination thereof to retain the mobile phone  108 . 
     Optionally, the mobile phone cover may be configured and arranged to receive and retail the holder  120 , or the holder  120  may be rigidly attached to the mobile phone cover. Holder  120  should be interpreted as one or more elements cooperating to allow the mobile phone  108  to be received and retained in the mobile phone cover. The holder  120  may be configured and arranged to accept a wide range of mobile phones  108 , or one or more specific types of mobile phone  108 . 
     Each charging station  110  is configured and arranged to receive and retain a rechargeable instrument  104 . For example, using one or more magnets, one or more mechanical retainers, one or more protrusions, one or more recesses, one or more fasteners, one or more openings, one or more resilient elements, one or more elastic elements, one or more clamps, one or more hooks, one or more threaded elements, one or more pins, one or more adhesive elements, one or more coatings, and any combination thereof to retain the rechargeable instrument  104 . 
     In  FIG. 1 , each charging station  110  comprises a recess, configured to receive the rechargeable instrument  104 . One or more magnets or mechanical retainers may be used, for example, to retain the rechargeable instrument  104 . I Each charging station  110  is configured and arranged to allow the rechargeable instrument  104  to be removed, either directly by hand, or using a simple tool, a mechanically operated release and/or an electrically operated release. Preferably, each rechargeable instrument  104  can be removed manually—for example, an EPTD can be manually removed from a charging station by tilting and grabbing the EPTD, or by tilting the EPTD and gliding it out of a magnetic slot of the charging station  110 . 
     In  FIG. 1  and  FIG. 8 , the mobile phone  108  comprises an energy supply, and the portable charging device  106  is configured and arranged:
         to transfer energy, in use, from the energy supply of the mobile phone  108 , placed in the holder  120 , to the two or more charging stations  110 ; and   to transfer energy, in use, from the charging stations  110  to the energy storage of the rechargeable instrument  104  placed in the respective charging station  110 .       

     The energy supply of the mobile phone  108  may comprise, for example, one or more rechargeable batteries. 
     By suitable configuration of the mobile phone cover and/or the portable charging device  106 , different types of rechargeable instruments  104  may be accommodated. For example, one or more rechargeable instruments  104  may be an implantable device, an implantable neurostimulation device, an EPTD  104 , a wearable device, a medical device, an implantable medical device (IMD)  102 , a therapeutic device, a medical aid, a cosmetic device, a device for stimulating one or more nerves (neurostimulator), a device for stimulating one or more muscles, a device for stimulating one or more organs, a device for stimulating spinal cord tissue, a device configured for powering wirelessly a further device, a device configured for powering wirelessly a further rechargeable instrument  104 , a personalized device, a custom-made device, a patient-specific device, a device for an individual, or any combination thereof. The rechargeable instrument  104  should not be construed as including one or more mobile phones  108 . 
     Covers and cases are known for receiving a one or more bank/credit cards—however, such a card, even smartcards, should not be considered as a rechargeable instrument  104  in the context of this disclosure. 
     Although smartcards may have a degree of energy storage, used by smartcard readers to read data from the card, they do not operate as intended once they leave the region in which energy is being received. In the context of this disclosure, a rechargeable instrument  104  is configured and arranged to retain an amount of energy in its energy storage such that the instrument  104  can substantially operate as intended for a significant period of time when it is no longer receiving energy from the storage device  106 . 
     In an alternative embodiment, the functionality of charging device  106  and mobile device  108  is combined in one apparatus. Furthermore, the charging device  106  may receive its energy from another source than the mobile device  108 —for example, the charging device  106  may further comprise a charging energy storage, such as one or more rechargeable batteries. The charging device  106  may optionally be configured and arranged:
         to transfer, in use, energy from the energy supply of the mobile phone  108 , placed in the holder, to the charging energy storage; and   to transfer, in use, energy from the charging energy to the two or more charging stations  110 .       

     In an alternative embodiment of the charging device, a charging station  106  is configured to receive and charge more than one rechargeable instrument  104 , such as more than one EPTD  104 . In this embodiment, the EPTDs in the charging station are charged simultaneously. 
       FIGS. 5 and 6  depict examples of nerves that may be stimulated using a suitably configured neurostimulation system  100  with an implantable distal end. It may provide neurostimulation to treat, for example, headaches or primary headaches. 
       FIG. 5  depicts the left supraorbital nerve  910  and right supraorbital nerve  920  which may be electrically stimulated using a suitably configured device.  FIG. 6  depicts the left greater occipital nerve  930  and right greater occipital nerve  940  which may also be electrically stimulated using a suitably configured neurostimulation system  100 . 
     Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the distal part of the stimulation device comprising stimulation devices  100  are depicted as regions:
         location  810  for left supraorbital stimulation and location  820  for right supraorbital stimulation for treating chronic headache such as migraine and cluster.   location  830  for left occipital stimulation and location  840  for right occipital stimulation for treating chronic headache such as migraine, cluster, and occipital neuralgia.       

     In many cases, these will be the approximate locations  810 ,  820 ,  830 ,  840  for the implantable part of the neuro stimulation system  100 . 
     For each implant location,  810 ,  820 ,  830 ,  840  a separate combinations of EPTD and IMD may be used. Where implant locations  810 ,  820 ,  830 ,  840  are close together, or even overlapping, a single stimulation system may be configured to stimulate at more than one implant location  810 ,  820 ,  830 ,  840 . A plurality of stimulation devices  100  may be operated separately, simultaneously, sequentially or any combination thereof to provide the required treatment. 
       FIG. 7  depicts further examples of nerves that may be stimulated using a suitably configured stimulation system  100  to provide neurostimulation to treat other conditions. The locations depicted in  FIG. 5  and  FIG. 6  ( 810 ,  820 ,  830 ,  840 ) are also depicted in  FIG. 7 . 
     Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the part of the stimulation device comprising stimulation electrodes are depicted as regions:
         location  810 ,  820  for cortical stimulation for treating epilepsy;   location  850  for deep brain stimulation for tremor control treatment in Parkinson&#39;s disease patients; treating dystonia, obesity, essential tremor, depression, epilepsy, obsessive compulsive disorder, Alzheimer&#39;s, anxiety, bulimia, tinnitus, traumatic brain injury, Tourette&#39;s, sleep disorders, autism, bipolar; and stroke recovery   location  860  for vagus nerve stimulation for treating epilepsy, depression, anxiety, bulimia, obesity, tinnitus, obsessive compulsive disorder, heart failure, Crohn&#39;s disease and rheumatoid arthritis;   location  860  for carotid artery or carotid sinus stimulation for treating hypertension;   location  860  for hypoglossal &amp; phrenic nerve stimulation for treating sleep apnea;   location  865  for cerebral spinal cord stimulation for treating chronic neck pain;   location  870  for peripheral nerve stimulation for treating limb pain, migraines, extremity pain;   location  875  for spinal cord stimulation for treating chronic lower back pain, angina, asthma, pain in general;   location  880  for gastric stimulation for treatment of obesity, bulimia, interstitial cystitis;   location  885  for sacral &amp; pudendal nerve stimulation for treatment of interstitial cystitis;   location  885  for sacral nerve stimulation for treatment of urinary incontinence, fecal incontinence;   location  890  for sacral neuromodulation for bladder control treatment; and   location  895  for fibular nerve stimulation for treating gait or footdrop.       

     Other conditions that may be treated include gastro-esophageal reflux disease, an autoimmune disorder, inflammatory bowel disease and inflammatory diseases. 
     IMD&#39;s  102  may be optimised for the stimulation of one or more nerves, one or more muscles, one or more organs, spinal cord tissue, brain tissue, one or more cortical surface regions, one or more sulci, and any combination thereof. 
       FIG. 2  shows a block diagram of an embodiment of an EPTD according to the present technology. The EPTD comprises an application specific IC (ASIC)  200 , a rechargeable battery and a transmission/receiving coil L 2  with or without a series-resonant capacitor. The ASIC comprises charger part  202 , a Wireless Communication Module (WCM) part  204 , a Logic control part  206  and a power amplifier (PA) part  208 . The charger part  202  comprises commonly known circuitry such as a rectifier, an up-converter, charger circuitry having constant current (CC) and constant voltage (CV) mode, battery monitoring and load control. The rechargeable battery can be any type of suitable rechargeable battery. The WCM part  204  comprises commonly known circuitry for Wireless Communication via the coil L 2 , such as a demodulator, modulator and a load-shift keying (LSK) signal generator. The WCM part  204  enables the EPTD  104  to communicate with the IMD  102  and the charging device  106 . The WCM part can be configured to apply any of the NFC standards, Qi interface standard or any other suitable proprietary wireless communication and energy transfer protocol. The Logic control part  206  comprises a pulse generator, control logic for controlling functions of the EPTD and a memory in which a number of IMD parameter sets are stored. An IMD parameter set comprises all control parameters an IMD needs to work properly and to apply a therapy. According to the present technology, each IMD parameter set comprises a unique identification code having a value linked to the unique identification code of an IMD  102 . In this way, the EPTD  104  knows which IMD parameter set has to be used for which IMD. The ASIC further comprises a power amplifier PA block comprising an amplifier and a matching circuit. A selector is used to switch between charging mode and IMD powering mode. In charging mode, the internal battery of the EPTD is charged. In IMD powering mode, power is transmitted to an IMD. In both modes, data transfer is possible. The EPTD is configured to send, preferably at regular intervals, a power signal to the IMD. The energy transferred in a power signal should be sufficient to enable the IMD to generate a stimulation pulse and to power the electronic circuitry of the IMD up to at least the next power signal. In an embodiment the power signal is a pulse-like signal. The EPTD can be configured to send a continuous power signal to the IMD. However, this has the disadvantage that unnecessary power is consumed by the IMD in the human body, which can cause heating of the tissue around the IMD. 
       FIG. 3  shows an example of block diagram of the IMD according to the present technology. This block diagram is not specific for the invention, other block diagrams can be devised. The IMD comprises an ASIC  300 , a transmission/receiving coil L 1  and one or more Electrodes (not shown). The ASIC  300  comprises an Overvoltage protection circuitry, tuning circuitry, a supply part  302 , a high voltage (HV) part  304 , a logic control part  306  and an NFC part  308 . 
     The supply part  302  comprises a rectifier, a HV buffer in the form of a capacitor, voltage measuring unit measuring the voltage of the HV buffer and controlling a Low-DropOut regulator and a low voltage buffer in the form of another capacitor. The Low-DropOut regulator supplies energy to the low voltage buffer. The capacity of the low voltage buffer is sufficient to power the logic control part  306  and NFC part  308  to at least the next power signal. The high voltage part  304  is configured to supply a stimulation pulse to the electrodes of the IMD. To perform this function, the high voltage part  304  comprises a current source, a current measuring unit and an electrode switch. The measured current is supplied to the logic control part  306 . The electrode switch is controlled by a switch control signal generated by the logic control unit  306 . The electrode switch enables to limit the amount of current of the stimulation pulse supplied to the electrodes. 
     The logic control part  306  comprises a memory to store the IMD parameter set, a unique identification code permanently stored in a memory location, a clock generator for generating a clock signal for the logic control unit, a counter for counting the number of clock cycles, a switch control signal generator a feedback circuit and a controller. The clock generator derives a clock signal from the RF frequency. As a result the clock signal of the EPTD and IMD will have the same clock frequency. The feedback circuit measures the current to the electrode(s) and determines a feedback signal to the EPTD to enable to EPTD to control the level of the power signal generated by the EPTD. In an embodiment to reduce the dimensions of the ASIC the memory to store the IMD parameter set is a volatile memory, along with a compact non-volatile memory to store the IMD identification code (e.g. using fuses). In another embodiment, at least a part of the IMD parameter set is stored in non-volatile memory. 
     The WCM part  308  comprises commonly known circuitry for Wireless Communication via the coil L 1 , such as a demodulator, modulator and a load-shift keying (LSK) signal generator. The WCM part  308  enables the IMD to communicate with the EPTD. 
     In general, the portable charging device further comprises a charging circuit, the charging circuit comprising one or more electrical components, configured and arranged to control charging in use. Optionally, one or more of these components may comprise one or more coils, configured and arranged to transmit and/or receive energy wirelessly. 
       FIG. 4  shows a block diagram of a first embodiment of a charging circuit  400 , comprised in the portable charging device  106 .  FIG. 8  schematically depicts the main interfaces of the charging circuit  400  with the other components of the portable charging device  106 . 
     The charging circuit  400  comprises a coil, connected to an input power part  402 , to wirelessly receive power from a mobile phone  108  by means of a suitable energy transfer protocol. For example, Qi, Powermat, Rezence, WiPower, Open Dots, PMA, Wireless Power Transfer (WPT), Simultaneous Wireless Information and Power Transfer (SWIPT), inductive coupling, resonant inductive coupling, capacitive coupling, and any combination thereof. The mobile device  108  comprises a corresponding coil  125 , configured and arranged to transfer energy to the input power part  402 . 
     Configuring and arranging one or more coils to transmit and/or receive energy wirelessly may require optimising one or more mechanical, electrical and/or magnetic parameters relevant for energy transfer. For example:
         current, voltage, energy charge and/or power supplied to the transmission coil;   frequency, waveform shape, repetition rate, operation duration of the transmission energy;   relative proximity, alignment and/or orientations of the transmitting and receiving coils;   relative dimensions of the transmitting and receiving coils;   the number of turns, the conductor materials used, the conductor thickness;   materials comprised in the cover, and in particular, in the charging station to increase energy transfer.       

     Optionally, the coil may be further configured and arranged to exchange data with the mobile phone  108  by means of a suitable wireless communication protocol, or a further coil may be so configured. For example, Bluetooth, Bluetooth LE, NFC, Low-power WAN, LTE, Qi, Wi-Fi, and any combination thereof. The coil  125  may be further configured and arranged to exchange data with the coil of the input power part  402 , or a further coil may be so configured. 
     Some protocols may allow both energy transfer and wireless communication to a suitable degree. 
     The charging circuit  400  further comprises the input power part  402 , and at least one charging station  110 . If optionally data is to be shared, the charging circuit  400  further comprises a WCM part  404 . 
     The charging circuit  400  associated with a charging station  100  comprises a charger part  408 ,  418 , and a coil  412 ,  422  configured and arranged for energy transfer. If optionally data is to be shared, the charging station part of the circuit  400  further comprises a WCM part  410 ,  420  and either a suitably configured coil  412 ,  422  or a further coil optimised for data communication. 
     A charging station  110  is configured to wirelessly transfer energy to the energy storage of the rechargeable instrument  104  placed in the respective charging station, for example to charge the rechargeable battery of an EPTD placed in the charging station. Optionally, data may be exchanged with the EPTD by means of the WCM part  404 . The WCM part  404  of the charging circuit  400  comprises commonly known circuitry of a demodulator, a modulator and a load-shift keying (LSK) signal generator. 
     The rechargeable element  104  further comprises a corresponding coil  115 , configured and arranged to receive energy from the energy transfer coils  412 ,  422  of the charging circuit  400 . 
     In summary, the portable charging device  106  is configured and arranged:
         to wirelessly transfer energy, in use, from the energy supply of the mobile phone  108 , placed in the holder, to the charging circuit  400 ;   to transfer energy through the charging circuit  400  (wired), in a predetermined and/or controlled manner, to two or more charging stations  110 ; and   to wirelessly transfer energy, in use, from the charging stations  110  to the energy storage of the rechargeable instrument  104  placed in the respective charging station  110 .       

     Optionally, the portable charging device  106  may be further configured and arranged, in use:
         to transfer data from the mobile phone  108  to one or more rechargeable instrument  104 ;   to receive data by the one or more rechargeable instrument  104  from the mobile phone  108 ;   to transfer data from one or more rechargeable instrument  104  to the mobile phone  108 ;   to receive data by the mobile phone  108  from the one or more rechargeable instrument  104 ;   to transfer data from a first rechargeable instrument  104  to a further rechargeable instrument  104 ;   to receive data by a further rechargeable instrument  104  from the one or more rechargeable instrument  104 );   and any combination thereof.       

     Optionally, the charging device  106  and the charging circuit  400 , may be configured and arranged to allow a degree of energy transfer between rechargeable instruments  104 . 
     For example, if one or more rechargeable instruments  104  comprise a further energy supply, the portable charging device  106  may be further configured and arranged:
         to wirelessly transfer energy, in use, from the further energy supply of the one or more rechargeable instruments  104  placed in a first charging station  110  to the charging circuit  400 ;   to transfer energy through the charging circuit  400  (wired), in a predetermined and/or controlled manner, to one or more further charging stations  110 ; and   to wirelessly transfer energy, in use, from the one or more further charging stations  110  to the energy storage of the rechargeable instrument  104  placed in the respective further charging station  110 .       

     Where required, the charging device  400  may be configured and arranged to control the charging in a predetermined and/or controlled manner. 
     According to an embodiment of the present technology, the IMD parameter set of an IMD is stored in volatile memory. As a result, the content of the IMD parameter set in the IMD is lost as soon as the low voltage buffer of the IMD is out of charge. The IMD is powered wirelessly by the EPTD. The EPTD generates at regular intervals a power signal to power the IMD. Depending on the implementation, during and/or after the generation of a power signal, the IMD and EPTD can exchange data. So when an EPTD is disconnected from an IMD, the IMD will be out of power very quickly as it does not receive power signals anymore. Consequently the IMD will lose any data stored in volatile memory and thus the IMD parameter set which is necessary to apply the correct treatment. To ensure that the treatment of headaches is not interrupted too long, the user must have at least two EPTDs. This allows the user to have always an EPTD with a fully charged rechargeable battery available for replacing an EPTD with an empty rechargeable battery. However if the user has two IMD for treatment of chronic headache, the EPTD could be combined with any of the two IMDs. However each IMD could have its own IMD parameter set defining the treatment to be applied. So to enable an EPTD to supply an IMD parameter set to any the EPTD in the medical system, the EPTD must have the IMD parameter set of at least all IMDs used in the system. Furthermore, the EPTD should not send to an IMD a parameter set that has to be used by another IMD. To ensure this, each IMD has its own unique IMD identification code permanently stored in an addressable location. Furthermore, in the EPTD, the IMD parameter set comprises an associated unique identification code. The unique identification code can be integral part of the IMD parameter set. It might also be possible that the EPTD stores in its memory a linkage between an IMD parameter set and a unique IMD identification code. 
     When an EPTD is magnetically coupled to an IMD, the EPTD will transmit a power signal to the IMD. The power signal will awake the IMD. After the IMD is activated, the IMD will be in not-connected mode. In not-connected mode, the IMD will transmit its unique identification code to the EPTD after the IMD is sufficiently powered by the power signal. The EPTD will receive the unique identification code and subsequently search in its memory for an IMD parameter set having an associated unique identification code which matches the unique identification code received from the IMD. If there is a matching identification code, the EPTD will transmit the associated IMD parameter set to the IMD together with the associated unique identification code. The IMD verifies whether the associated unique identification code corresponds to its own unique identification code. If there is a match, the IMD will switch to connected mode. If there is not a match, the IMD stays in non-connected mode. As a result, the IMD will retransmit to the EPTD its unique identification code after the receiving a subsequent power signal. In connected mode, the IMD could regularly transmit its current parameter set to EPTD. In this way, also adjustment of the IMD parameter set by the IMD is regularly updated in the corresponding IMD parameter set stored in the memory of the EPTD. In this way, the EPTD stores an actual IMD parameter set in its memory. 
     In the portable charging device  106 , the following method is applied. When an EPTD is positioned in a charging station  110  of the charging device  106 , the charging device  106  will request to transmit at least the IMD parameter set that has been transmitted to an IMD after the last recharging action of said IMD. This IMD parameter set may have parameter values that have been modified by the IMD during the period that the EPTD had powered the IMD. In an embodiment, the IMD parameter set comprises a time stamp indicating the time when the latest modification was made or the time when the EPTD most recently received the IMD parameter set from the IMD. 
     Optionally, the portable charging device  106  may further comprise one or more memory components, configured and arranged to store and/or distribute one or more parameter sets of data. Optionally, one or more memory components may be comprised in the charging circuit  400 . 
     After receipt of an IMD parameter set from the EPTD, the charging device  106  may update the IMD parameter set in its own parameter set memory. The updating may depend on the time stamp of the IMD parameter set. In an embodiment, an IMD parameter set is only replaced by a new IMD parameter set when the time stamp of the new parameter set from the IMD is later in time than the time stamp of the parameter set currently stored in a parameter set memory of the charging device  106 . It should be noted that each parameter set stored in the parameter set memory of the charging device has a corresponding unique IMD identification code. 
     After the charging device  106  has received a new IMD parameter set, the charging device  106  distributes the parameter set to all EPTDs that are (or will be) located in the other charging stations. In this way, all EPTDs will have the same IMD parameter sets stored in its memory. In an alternative embodiment, the charging device  106  distributes all parameter sets stored in its parameter set memory to all EPTDs located in the charging stations  110 . In this alternative embodiment, all EPTDs located in the charging device  106  will have the same IMD parameter sets for all IMD used in the medical system. Thus when an EPTD is placed in a charging station  110  of the charging device  106 , the charging device  106  first obtains at least the IMD parameter sets from the EPTD which content has been changed after its last removal from the charging device  106 . Subsequently, the charging device  106  transmits all the IMD parameter sets stored in its parameter set memory to the last placed EPTD in the charging stations  110  to update the IMD parameter sets in the EPTD. Furthermore, the charging device  106  transmits at least the IMD parameter sets that have been updated after obtaining the IMD parameters from the EPTD after placement in a charging station  110  to the EPTDs located in the other charging stations. Thus it might be possible that when an EPTD that has not been used for a long time is placed in the charging device  106 , the changed IMD parameters sets that are submitted to the charging device  106  are not used to update the corresponding IMD parameter sets stored in the parameter set memory of the charging device  106 . This is due to the fact that the time stamps associated with the IMD parameters sets from the EPTD indicate a moment in time which is before the moment in time indicated by the time stamps associated with corresponding IMD parameter sets having the same unique identification code and stored in the parameter set memory of the charging device  106 . Consequently, the charging device  106  will only update the IMD parameter sets in the EPTD that has not been used for a long time. 
     As described above, the EPTD generates a pulse shaped power signal. In an embodiment, the IMD controls which part of the pulse shaped power signal is passed to the electrodes of the IMD to form the stimulation pulse. So the EPTD determines when a stimulation pulse could be supplied to the electrodes and the IMD controls the beginning and end of the stimulation pulse. In an alternative embodiment, the IMD comprises a pulse generation module and pulse energy storage with a capacity that is sufficient for the IMD to generate a burst of stimulation pulses with a duration sufficient to apply a therapy according to the IMD parameter set. To be sure that the EPTD and IMD uses the same IMD parameter sets to generate the stimulation pulse, the EPTD sends every now and then a command to the IMD comprising a unique identification code associated with the IMD parameter set which the EPTD is using to generate the power signals. If the unique IMD identification code in the command transferred from the EPTD to the IMD differs from the unique IMD identification code of the IMD parameter set which the IMD currently is using to form the stimulation signal, the IMD will detect this and it will change to the status of the IMD from connected mode to not-connected mode. In this way, the risk that incorrect stimulation pulses will be supplied to the electrodes is reduced significantly. For the same reason in an embodiment, the IMD is configured in connected mode to transmit intermittently its unique IMD identification code to the EPTD. The EPTD will check whether said unique IMD identification code matches with the IMD identification code of the IMD parameter set that the EPTD uses to generate the power signals at regular intervals. In an embodiment, after detection of a mismatch, the EPTD stops with the generation of subsequent power signals for a predetermined time to force the IMD to run out of charge such that the IMD content of its memory is cleared and the IMD begins to transmit its IMD identification code to the EPTD. After receipt of the IMD identification code by the EPTD, the EPTD will transmit the IMD parameter set associated with the same IMD parameter code to the IMD. As a result the EPTD and IMD use the parameter sets having the same IMD identification code. 
     As described before, the memory of the IMD can be a volatile memory. Furthermore, there might be periods in time wherein no stimulation pulses are supplied to the electrodes of the IMD and/or no communication between the EPTD and IMD has to take place in the time period between two power signals. For that case, the IMD has an ultra-low power mode. In ultra-low power mode of the IMD, only the clock generator generates a clock signal to keep the IMD alive to the next power signal. The energy storage in the capacitor to power the electronics is chosen such that the IMD stays alive up to at least the next power signal. In an embodiment, the period of time to stay alive in low power mode is a device specific parameter permanently stored in the IMD. This parameter is submitted to the EPTD to define at the EPTD the period of time between two charging pulses. Furthermore, IMD could transmit a parameter to the EPTD which is indicative for the energy storage capacity of the capacitor for powering the electronics of the IMD. This parameter is used to limit the energy of a power signal in case no stimulation pulse has to be supplied to the electrode(s) of the IMD. In other words, the IMD is configured to operate at least in a first operating mode (ultra-low power) and a second operating mode (normal operation). The EPTD is configured to determine the operating mode of the IMD, and to generate power signals with a time interval between two power signals depending on the determined operating mode of the IMD. The IMD further comprises an energy storage with an energy storage capacity that enables the IMD to hold the data stored in the volatile memory for more than one time interval and preferably not more than two time intervals, wherein the time interval is defined by the operating mode determined by the EPTD and parameters related to the energy storage capacity and energy consumption of the electronics of the IMD in the respective modes. It should be noted that said parameters can be stored in the IMD parameter set as each IMD comprises its own parameter set which is linked to the unique IMD identification code. 
     So, If the period of no communication/no stimulation lasts longer than the energy stored in the capacitor allows in ultra-low power mode, a short power signal with low amplitude can be given to recharge the capacitor instead of a power signal that is also suitable to supply a stimulation pulse to the electrodes. The later power signal has a high amplitude for a longer time. 
     In another embodiment, the IMD is configured to communicate with the EPTD about the energy stored in the capacitor for powering the electronics of the IMD and optionally the pulse energy storage for generating of the stimulation pulses internally by the IMD. This embodiment enables the IMD to control the characteristics of the power signal generated by the EPTD, such as but not limited to: amplitude, pulse width and length of the power signal. 
     In an embodiment, the EPTD generates a continuous power signal. In this embodiment, the IMD will transmit in not-connected mode at regular intervals it unique IMD identification code. After receiving an IMD parameter set including said unique IMD identification code, the IMD switches to connected mode. 
     In an alternative embodiment, the EPTD transmits wirelessly all IMD parameter sets stored in its memory when the EPTD detects that an IMD receives power from the EPTD. In this embodiment, the IMD receives all IMD parameter sets transmitted by the EPTD. The IMD retrieves from each IMD parameter set the unique identification code included in said IMD parameter set. When the retrieved unique identification code matches its own unique IMD identification code, the IMD deploys said parameter set to enable the IMD to provide the electrical stimulation defined by the IMD parameter set to the body where the IMD is implanted. 
     In an embodiment, the charging device  106  and/or comprises a user interface to adapt the IMD parameter sets. If there is no user interface on the EPTD, the charging device  106  may also pass on adapted parameter sets to the EPTD, and the charging device  106  may make adjustments based on user feedback (e.g. a smartphone user interface where the patient indicates how effective a therapy has been) or based on usage information (how long did the user actually use the EPTD). The usage information can also be read by the charging device  106  from the EPTD). 
     In the embodiments described above, the IMD is a neuro stimulation device. The presented technology can also be used in implants for other applications that control electronically for example micro valves or pumps implanted in a body. 
     In many applications where rechargeable instruments  104  are used, common problems including the user forgetting to recharge the instruments  104  and/or the user having too little time to fully recharge the instruments  104 . 
     Especially where the rechargeable instruments  104  are used for a personalized application, such as a personalised therapy, stimulation or medical use, users become more reliant and dependent on the correct operation of these instruments, resulting in a severe inconvenience if they are not sufficiently charged. In this context, personalized means that the instruments  104  are optimised for a few users—in other words, in case of a defective personalized rechargeable instrument  104 , the user has very few possibilities to find a replacement. The personalized rechargeable instruments  104  are unlikely to be available for immediate use as mass-produced devices, commodity devices, or off-the-shelf items. 
     The degree of personalization is greatly increasing, which makes the inconvenience worse. In some cases, where the rechargeable instruments  104  are custom-made, patient-specific or patient-adaptable, the rechargeable instruments  104  should only be used by one user or an individual—if used by others, the rechargeable instruments  104  may just operate incorrectly. However, in some critical cases, the use by others may even pose a substantial health risk. 
     In systems where critical functionality is divided over two or more devices, and one of these is a rechargeable instrument  104  for powering (either wired and/or wirelessly) a further device (for example, an EPTD  104  and IMD  102 ), the degree of inconvenience is similar as these two or more devices must be paired to a high degree. Dividing the functionality over a plurality of devices may increase the chance that one of these devices is not operable or even forgotten as there are more devices to keep track of. In addition, dividing the function may result in smaller devices, which are even more likely to be lost. 
     Custom-made means that it is intended to address a specific anatomo-physiological features or pathological condition of the individual (or user) for whom it is intended. Patient-specific means that it is produced based on a standard device template model, or specified design envelope (e.g., minimum and maximum dimensions, performance limits, and other clinically relevant factors), that is matched to a patient&#39;s anatomy using techniques such as scaling of the device based on anatomic references, or by using the full anatomic features from patient imaging. Patient-adaptable means that it is a mass-produced medical device that must be adapted or assembled at the point of care, in accordance with the manufacturer&#39;s instructions, to suit an individual&#39;s specific anatomo-physiologic features prior to use. Mass-produced means identical devices that are produced in continuous production runs or homogenous batches. 
     By providing a portable charging device  106  in a mobile phone cover there is a reduced risk that an instrument will not work properly when the user wishes to use it. In addition, there may also be lower chance that the user will forget to take the rechargeable instruments with them when they are travelling and/or away from home. Most users will reliably charge their phone  108 , and are used to taking it with them when they are travelling and/or away from home. 
     Additionally, many mobile phones  108  are dimensioned to be portable, particularly commercially available mobile phones  108 . 
     Preferred dimensions for the mobile phone cover are those suitable for transport in a small bag, and most preferably pocket-sized. 
     Smaller dimensions should preferably be used, as this may increase portability and may increase the likelihood that the user will use the cover regularly, preferably every day. 
       FIG. 11  depicts schematically a further embodiment of a charging circuit  3400  comprised in a further embodiment of a charging device  3106 . 
     The charging device  3106  is the same as that depicted in  FIG. 8 , except for:
         the charging circuit  3400  does not comprise one or more coils to receive energy from the mobile phone  108 ;   the charging circuit  3400  does not comprise one or more coils to transfer energy to the two or more charging stations  3110 ; and   the charging circuit  3400  does not transfer charging energy through itself (wired) from the mobile phone  108  to the two or more charging stations  3110 .       

     In other words, the portable charging device  3106  is configured and arranged:
         to wirelessly transfer energy, in use, from the energy supply of the mobile phone  108 , placed in the holder, to the energy storage of the rechargeable instruments  104  placed in the charging stations  3110 .       

     Where required, the charging device  3400  may be configured and arranged to control the charging in a predetermined and/or controlled manner. 
     By suitable configuration and arrangement of the energy transfer coil  3125  comprised in the mobile phone  108 , the holder  3125  of the mobile phone  108 , the two or more charging stations  3110 , and the energy reception coils  3115  comprised in the one or more rechargeable instruments  104 , a charging circuit  3400  may be made optional. Additionally or alternatively, the control of the charging in a predetermined and/or controlled manner may be performed using a software app, running on the mobile phone  108 . 
       FIG. 10  depicts schematically another embodiment of a charging circuit  2400  comprised in a further embodiment of a charging device  2106 . 
     The charging device  2106  is the same as that depicted in  FIG. 11 , except for:
         the charging circuit  2400  comprises one or more electrical interconnections and/or electrical connectors  1125 , configured and arranged to connect to the mobile phone  108  when placed in the holder  2120 , and further configured and arranged to transfer energy wired from the energy supply of the mobile phone  108  to the charging circuit  2400 ;   the charging circuit  2400  comprises a coil  2125  to transfer energy wirelessly from the charging circuit  2400  to the two or more charging stations  2110 ; and   the two or more charging stations  2110  comprises a coil  2115  and one or more electrical interconnections and/or electrical connectors  1115  to receive energy wirelessly from the charging circuit  2400 , and to transfer energy wired to the respective rechargeable instrument  104 .       

     In this embodiment  2106 , it is not necessary that the mobile device  108  comprises an energy transfer coil as the energy is transferred using the coil  2125  comprised in the charging circuit  2400 . However, it may be advantageous to use a mobile device with an energy transfer coil, and to transfer energy at substantially the same time that energy is transferred by the energy transfer coil  2125  of the charging circuit  2400 . 
     Similarly, it is not necessary that the rechargeable instruments  104  comprise an energy receiving coil as the energy is transferred using the energy receiving coil  2115  and the interconnections and/or connectors  1115  (also called galvanic contacts) comprised in the charging station  2110 . 
     Where required, the charging device  2400  may be configured and arranged to control the charging in a predetermined and/or controlled manner. 
       FIG. 9  depicts schematically yet another embodiment of a charging circuit  1400  comprised in yet a further embodiment of a charging device  1106 . 
     The charging device  1106  is the same as that depicted in  FIG. 10 , except for:
         the charging circuit  1400  comprises further electrical interconnections and/or electrical connectors  1115 , configured and arranged to connect to the mobile phone  108  when placed in the holder  1120 , and further configured and arranged to transfer energy wired from the energy supply of the mobile phone  108  to the charging circuit  1400 ; and   the charging circuit  1400  comprises further electrical interconnections and/or electrical connectors  1115 , configured and arranged to connect to the two or more rechargeable instruments  102  when placed in the charging stations  1110  to transfer energy wired from the charging circuit  1400 .       

     In this embodiment  1106 , it is not necessary that the mobile device  108  comprises an energy transfer coil as the energy is transferred using the interconnections and/or connectors  1115  comprised in the charging circuit  1400 . Similarly, it is not necessary that the rechargeable instruments  104  comprise an energy receiving coil as the energy is transferred using the interconnections and/or connectors  1115  comprised in the charging circuit  1400 . 
     Where required, the charging device  1400  may be configured and arranged to control the charging in a predetermined and/or controlled manner. 
     A further problem with rechargeable instruments  104 , and in particular, personalized rechargeable instruments, is the desire by a user for discretion. A user or individual may wish to transport and charge the instruments  104  without revealing their presence to others. In particular, when the rechargeable instruments  104  are configured for one or more therapeutic, stimulation and/or medical uses, the user may not wish others to be aware that they have a condition which requires treatment. 
     The mobile phone cover as disclosed herein may be modified to provide inconspicuous and unobtrusive storage and charging.  FIG. 1  depicts a mobile phone cover in perspective view, and  FIG. 12  depicts a portion of the same mobile phone cover schematically after the mobile phone  108  has been placed in the holder  120 . 
       FIG. 12  shows the holder  120  portion of the mobile phone cover as viewed from directly above the screen size or the back size of the mobile phone  108 . Preferred is the mobile phone cover is configured and arranged such a user may view at least a portion of the mobile phone  108  display when the mobile phone  108  is retained in the mobile phone cover—in other words, when the view of  FIG. 12  is considered as viewed directly from above the screen side. This allows at least some functions of the mobile phone  108  to be used normally. 
     The mobile phone cover includes a retaining surface comprising the two or more charging stations  110 . As depicted in the example of  FIG. 1  and  FIG. 12 , this is the upper surface of the portable charging device  106 . 
     In general:
         the holder  120  comprises one or more mobile phone  108  retainers, configured and arranged to releasably receive and retain the mobile phone  108  such that the visibility of at least a portion of the mobile phone cover is restricted when the mobile phone  108  is retained in the holder  120 ; and   one or more rechargeable instrument  104  retainers, configured and arranged to releasably receive and retain the one or more rechargeable instruments  104  in a charging station  110 , wherein the one or more charging stations  110  are comprised in the restricted visibility portion of the mobile phone cover such that the visibility of the retained rechargeable instruments  104  is restricted when the mobile phone  108  is retained in the holder  120 .       

     In the example of  FIG. 1  and  FIG. 12 , the holder  120  provides two holding functions  120   a ,  120   b:    
     holder  120   a =configured and arranged to releasably receive and retain the mobile phone  108  (for example, by using one or more mechanical retainers), and 
     holder  120   b =configured and arranged to be releasably retained by the retaining surface of the portable charging device  106  (for example, by using one or more magnets). 
     As depicted, the mobile phone  108  is retained in the holder  120   a  when holder  120   b  is released from the mobile phone cover. 
     Alternatively, the holder  120  may be integrated with the retaining (upper) surface of the portable charging device  106  to provide one holding function. The mobile phone  108  is then released from the holder  120  when it is released from the mobile phone cover. 
     When the mobile phone  108  is retained in the mobile phone cover, visibility of a portion of the upper surface of the charging device  106  is restricted, and the charging stations  110  are comprised in the portion with restricted visibility. In other words, the mobile phone  108  covers the accessible part of the two or more charging stations  110  when it is retained in the mobile phone cover. The approximate locations of the charging stations  110  covered by the mobile phone  108  are depicted in  FIG. 12 . 
     Many different types of retainer configurations which may be used, allowing a higher or lower degree of release. For example, the holder  120  may be configured and arranged to slide over the retention surface to reveal the charging stations  110 . Additionally or alternatively, one or more rotation points may be used. Additionally or alternatively, one or more hinges may be used. 
     Optionally, different degrees of release may be provided, allowing one or more charging stations  110  to be revealed. 
     Preferably, the visibility of substantially all outer surfaces of the two or more rechargeable instruments  104  is restricted when the mobile phone  108  is retained in the mobile phone cover by being retained in the holder  120 . 
     This provides a very high degree of discretion as the rechargeable instruments  104  are hidden, allowing the user to transport them covertly. 
     The mobile phone cover providing charging and storage as depicted in  FIG. 1 , may be further configured and arranged to comprise any of the portable charging devices disclosed herein, such as the depicted embodiments  1106  in  FIG. 9, 2106  in  FIG. 10, and 3106  in  FIG. 11 . The relative positions of the retained mobile phone  108  and retained rechargeable instruments  104  may be configured and arranged depending on the requirements of the charging circuits  400 ,  1400 ,  2400 ,  3400 . For example, when implementing the example of  FIG. 11 , it may be advantageous to minimise the distance between energy transfer coil  3125  comprised in the mobile phone and the energy receiving coils  3115  comprised in the two or more rechargeable instruments  104 . 
       FIG. 13  depicts a portion of a further embodiment of a mobile phone cover schematically after the mobile phone  108  has been placed in a holder  120 ,  1120 ,  2120 ,  3120 .  FIG. 13  shows the holder  120 ,  1120 ,  2120 ,  3120  portion of the mobile phone cover as viewed from directly above the screen side or the back side of the mobile phone  108 . The mobile phone cover includes a retaining surface comprising the two or more charging stations  110 ,  1110 ,  2110 ,  3110 . This is the upper surface of the portable charging device  106 ,  1106 ,  2106 . 3106 . 
     It is the same as depicted in  FIG. 12 , except:
         the portable charging device  106 ,  1106 ,  2106 ,  3106  further comprises one or more drawers, allowing one or more charging stations  110 ,  1110 ,  2110 ,  3110  to be revealed without releasing the mobile phone  108 . As depicted, a single drawer is used to reveal and/or cover (conceal) four charging stations  110 ,  1110 ,  2110 ,  3110 , but any suitable number of drawers may be used. It may be advantageous to provide one drawer for each charging station  110 ,  1110 ,  2110 ,  3110 .       

       FIG. 14  depicts a portion of a further embodiment of a mobile phone cover schematically after the mobile phone  108  has been placed in a holder  120 ,  1120 ,  2120 ,  3120 .  FIG. 14  shows the mobile phone cover as viewed from directly above the screen side or the back side of the mobile phone  108 . The mobile phone cover comprises two main sections:
         a holder  120 ,  1120 ,  2120 ,  3120  portion for retaining the mobile phone  108 , depicted on the right, and   the charging station  110 ,  1110 ,  2110 ,  3110  portion of the portable charging device  106 ,  1106 ,  2106 ,  3106 , depicted on the left.       

     As depicted, the mobile phone cover is open. These sections are connected using one or more hinges, and the mobile phone cover is closed by rotating the charging station section about the one or more hinges. 
     In this example, one or more charging stations  110 ,  1110 ,  2110 ,  3110  may be at least partially visible when the mobile phone cover is open. In this example, the visibility of the retained rechargeable instruments  104  is restricted when the mobile phone  108  is retained in the holder  120 ,  1120 ,  2120 ,  3120  and the mobile phone cover is closed. 
     Optionally, the holder  120 ,  1120 ,  2120 ,  3120  may be further configured and arranged to provide a second holding function, namely to receive and hold the mobile phone cover closed. 
     While the invention has been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon reading the specification and upon study of the drawings. It must be understood that this description is given solely by way of example and not as limitation to the scope of protection, which is defined by the appended claims. 
     For example, it may be advantageous for the mobile phone cover to further comprise one or more software, mechanical, electrical, optical or acoustic elements to indicate to a user that one or more rechargeable instruments  104  are retained in a charging station  110 ,  1110 ,  2110 ,  3110 . Additionally or alternatively, an empty charging station  110 ,  1110 ,  2110 ,  3110  may also be similarly indicated. It may be advantageous for the occupancy status of the charging stations to be indicated using a software app, running on the mobile phone  108 . 
     Additionally or alternatively, it may be advantageous for the mobile phone cover to further comprise one or more software, mechanical, electrical, optical or acoustic elements to indicate to a user the charging states of one or more rechargeable instruments  104  retained in a charging station  110 ,  1110 ,  2110 ,  3110 . Additionally or optionally, the discharge state and/or estimated usage time may also be similarly indicated. It may be advantageous for the charge/discharge/usage status of the rechargeable instruments  104  to be indicated using a software app, running on the mobile phone  108 . 
     Optionally, the charging stations may be further configured and arranged to allow convenient cleaning by a user. This is particularly advantageous when the rechargeable instruments  104  are configured for use, either directly or indirectly, in one or more therapeutic, stimulation and/or medical uses. 
     In a further example, a mobile phone cover may comprise:
         a holder  120 ,  1120 ,  2120 ,  3120  for receiving and retaining a mobile phone  108 ;   portable charging device  106 ,  1106 ,  2106 ,  3106  having two or more charging stations  110 ,  1110 ,  2110 ,  3110  and an energy supply, each charging station  110 ,  1110 ,  2110 ,  3110  being configured and arranged for receiving and retaining a rechargeable instrument  104 , the rechargeable instrument  104  comprising an energy storage;       

     the portable charging device  106 ,  1106 ,  2106 ,  3106  being further configured and arranged:
         to transfer energy, in use, from the energy supply of portable charging device  106 ,  1106 ,  2106 ,  3106  to the two or more charging stations  110 ,  1110 ,  2110 ,  3110 ; and   to transfer energy, in use, from the charging stations  110 ,  1110 ,  2110 ,  3110  to the energy storage of the rechargeable instrument  104  placed in the respective charging station  110 ,  1110 ,  2110 ,  3110 .       

     By providing an energy supply in the portable charging station, this may further reduce the risk that the instruments  104  will not work properly or be inoperable when the user requires it. The rechargeable instrument  104  should not be construed as including one or more mobile phones  108 . 
     Alternatively, the energy supply of the portable charging device  106 ,  1106 ,  2106 ,  3106  may comprise one or more rechargeable batteries. This may allow the portable charging device  106 ,  1106 ,  2106 ,  3106  to be charged by an external charging device. In this example, the external charging device should not be construed, in this example, as including the mobile phone to be received and retained in the mobile phone cover. 
     In a further example, any of the mobile phone covers described herein may have a first and second outer surface, extended longitudinally and extended transversely, the thickness being determined by a perpendicular distance between corresponding points on the first and second outer surfaces, the mobile phone cover having a maximum thickness of 2 cm or less, preferably 1 cm or less, more preferably 0.5 cm or less. 
     There is a growing need to transport smaller instruments, particularly when these are personalised. A thinner-dimensioned cover may mean that the user is more likely to use the cover regularly, preferably every day. It may also further increase portability.