Where does a tag go in a product with a battery or a metal body?
Against a non conductive part of the housing, with ferrite behind it where metal or a cell sits close, and at a spot a hand can reach squarely. The decision belongs in the mechanical design, because every option left once the tooling exists is worse than the one taken before it.
What the body does to the field
A conductive surface in an alternating field develops currents that oppose it, and it shifts the antenna away from the frequency it was tuned to. The metal page sets out both mechanisms; what matters to a product designer is that they stack, and that the result is a tag which does nothing rather than a tag which reads a little less far.
That abruptness is why this is a design question and not a tuning question. A tag reads on the bench, the same tag reads nothing in the assembled product, and there is no intermediate state to optimise.
Paint, anodising and print do not change it, since the conductor is underneath. Neither does a metallic decorative finish on a plastic housing: a vacuum metallised bezel or a foil stamped logo over the antenna is metal as far as the field is concerned.
A cell is a metal object
A battery behaves like the housing. It is conductive, it is usually the largest flat object inside a product, and it tends to occupy the face a designer would most like to put the tag on.
Two more parts belong on the same list. A wireless charging coil has a ferrite shield of its own and a coil that couples with anything nearby, which the charging page covers and the troubleshooting page sees in the field. A display and its frame are metal in the places that matter.
So the useful question in a mechanical review is not whether the product is metal, it is what lies in the few millimetres behind the intended tap point.
Where the tag can go
A non conductive window in the housing. A moulded insert, a base pad, a plastic end cap or a battery door, with the tag directly behind it. The window has to be non conductive over the whole antenna area rather than over its centre.
An on metal construction. A ferrite layer between the antenna and the metal redirects the field instead of letting it be cancelled, which the on metal page describes. It costs thickness, a few tenths of a millimetre at least, and a slim product may not have it to give. A foam spacer is not a substitute, as the spacer page measures.
Outside the product. A hangtag, a label on the packaging or a card in the box reads perfectly and is a different decision, with consequences the carrier page sets out: a carrier that leaves with the packaging is not on the product any more.
Deciding it before the tool
Put the tap point in the mechanical drawing, with the tag, its clearance and its marking. The mark matters as much as the placement, because people aim at a marked spot and wave at a blank surface, which the signage page found to be the highest return change in any deployment, and the marks page covers what may be printed there.
Then prove it on an assembled sample rather than on the component, which the prototype page sets out step by step.
What makes this worth doing early is the shape of the alternatives. Once the tool is cut, the remaining moves are to put the tag on the packaging, to accept a tap that only some phones manage, or to modify the tool. The first two are visible to every customer and the third is the expensive one.
Frequently asked questions
Can a tag sit directly on a battery?
No. A cell is a conductive body like the housing, so it needs either a ferrite backed construction or a different location.
Does the window have to be an opening?
It has to be non conductive over the antenna, not empty. A moulded insert or a base pad works; painted metal does not, since the conductor is under the paint.
Does an on metal tag solve everything?
It solves the surface. It costs thickness and money, and a product with no room behind its face still has a placement problem.
Where should the tap point be?
Somewhere a hand reaches squarely, marked, and away from metal and the cell. Phones differ in antenna position, so the marked area should be generous.