# How realistic would charging batteries with inductive power transmission be?

I've read articles on inductive charging and related stuff on Wikipedia and now I wonder - what if I wanted to develop a battery (also a matching charger and the battery compartment) with completely insulated terminals that gives/accepts power via induction as in an inductive charging system? How practical would such battery be?

• I think it is a good idea and practical. Especially in battery pack design. – user4888 Jul 4 '11 at 12:51
• You just have to keep the inductive element away from the cell electrodes in a pack. – Mike DeSimone Jul 4 '11 at 15:26

## 2 Answers

Efficiency could be a bit of a problem.

The induction power transfer is done through a high frequency EM field. This transfer is not 100% efficient as it radiates energy in other directions (careful design could increase transfer efficiency, but you'll never get a perfect transfer). The generation of the HF EM field consumes energy.

Therefore, you may get at best 80% $^*$ of the energy transferred from the battery to the device.

Then there is the cost. It's not a cheap system compared to what is essentially a bit of metal that is used currently.

Combine the two and what is maybe a 99.999% efficient piece of metal would be being replaced by a complex circuit costing many dollars and reducing the efficiency to maybe 75%.$^*$

Then of course, if the device is switched off, the battery will still be consuming power in generating a HF EM field that is not being used, so there would need to be a way for the device to turn off the battery - and turn it on again without any power (most easily done with good ol' wires...)

So nice as it would be, I can't see it really being practical.

$^{*}$These efficiencies are just made up off the top of my head and not to be quoted as accurate.

It will be problematic at best. Batteries are similar to capacitors in that you want to maximize electrode surface area inside the cell, while minimizing electrode volume, since the electrode doesn't itself store energy.

This large area of conductive material can develop eddy currents in the presence of an alternating magnetic field, dissipating a significant amount of inducted energy as heat. This heat will also serve to shorten the battery's life, and in the case of lithium batteries, reduce charge rate since the battery's temperature must be monitored and kept below a certain level, lest you start a fire.

Eddy currents are also a problem for high-current windings in planar transformers and foil windings in regular transformers. They are strongest near the transformer's gap.