Wireless power transfer promises sealed, connector-free products - and NiMH, with its tolerance and safety profile, is a plausible battery for such designs, from waterproof consumer devices to sealed industrial sensors and medical accessories. Yet wireless charging adds a control problem between the source and the cell: coupling varies with alignment and gap, the receiver must still deliver a controlled constant current, and coil losses create heat and obscure the voltage/temperature signals on which NiMH termination depends. This paper assesses inductive and resonant wireless charging as applied specifically to NiMH, works through the receiver architecture needed to preserve current-controlled charging and valid termination, and identifies where wireless NiMH is advantageous and where the added complexity is not justified.
Wireless transfer couples a transmitter coil to a receiver coil by magnetic field; tightly coupled inductive systems operate efficiently only at close, aligned range, while resonant (loosely coupled) systems tolerate greater gap and misalignment by tuning both sides to a common frequency. The receiver rectifies the induced AC and regulates it to the battery; efficiency peaks in a designed operating region and falls with misalignment, distance and loading.
For a battery charger the link is simply a variable, lossy DC-DC stage preceding the actual charge controller; its variability is the new design challenge, because the power reaching the cell is not the power the transmitter commands.
NiMH requires controlled charge current (Paper 15), so the wireless receiver must regulate output current despite coupling variation - achieved by a receiver-side regulating stage (controlling the rectified bus to a current loop), transmitter-side control informed by receiver feedback (in-band or out-of-band communication), or both in a closed wireless power system. Without regulation, coil movement would modulate charge current and corrupt -delta-V, which is only valid at stable current (Paper 6).
Qi-style and proprietary wireless-power controllers increasingly integrate this closed-loop power control; the battery-charge function then sits behind a reasonably stable supply and reuses the standard NiMH state machine, with the link treated as another power-stage element in the sense of Paper 36.
Coil and receiver losses become heat inside the sealed product, often adjacent to the cells, which both warms the battery and contaminates the dT/dt termination signal - the charger must distinguish recombination heating in the cell from link losses in the coil. Solutions include separating the NTC thermistor (thermally coupled to cells, isolated from coil, Paper 38), modelling link efficiency to subtract its known losses, and derating charge power when the combined temperature approaches limits.
Because sealed products cannot convect heat freely, the wireless case intensifies the pack thermal discipline of Paper 28; charge current is often set by total enclosure thermal budget rather than the cell's intrinsic fast-charge ceiling.
A wireless NiMH charger still terminates on -delta-V, dT/dt, absolute temperature and time, evaluated on the cell-side current and temperature; the receiver controller communicates charge status and power requests to the transmitter and commands power down at termination and during maintenance. Pulse maintenance (Paper 9) maps naturally to wireless: brief power pulses at low duty minimise both overcharge and link standby losses, and the transmitter can fully switch off between them.
Robust designs handle loss-of-coupling mid-charge (pause and hold state), foreign-object detection required by wireless-power safety, and a fault path that removes transmitter power if receiver feedback is lost - preventing a driven-but-unregulated primary.
The strongest cases are sealed/waterproof products where connectors are a reliability or hygiene liability, sealed industrial and medical accessories, devices charged in docking cradles where alignment is fixed (which makes inductive efficiency high and predictable), and high-utilisation fleets of small devices. It is weakest where high fast-charge power is needed in a small enclosure (link heat dominates), where alignment is uncontrolled, or where a simple contact charger would meet the need at far lower cost and higher efficiency.
The first figure diagrams the wireless-to-cell control chain; the second sequences a wireless charge including coupling feedback and cell-side termination, showing where standard NiMH logic is preserved.
A wireless NiMH project selects the wireless-power standard/controller, designs coils for the alignment geometry, places a current-regulated receiver feeding the NiMH charge state machine, thermally separates coil and cell sensing, and validates termination across misalignment and gap as well as temperature. Weijiang supplies the cell charge and thermal envelopes that set the sustainable wireless power level and supports co-validation of the cell-side profile. The final frontier paper considers the most ambitious control concept - the battery digital twin.
Weijiang Power designs and manufactures nickel-metal hydride cells, matched packs and charging-ready configurations for consumer, industrial, medical and mobility customers, and supports partners with charge-protocol guidance, IEC 61951-2 performance files, IEC 62133-1 safety evidence and charger co-validation. Share your cell format, charge rate, thermal envelope and cycle target and our engineers will specify a cell-and-charge combination that protects both runtime and service life. Review the range on the products page.
