Here's a variation on this theme:
If someone orders an electronic device which contains a lithium battery, it can be posted quite legally via Royal Mail or any courier service provided the battery is inside the device. But if you order a battery on its own, it cannot legally be sent by post or couriered.
This means buying a replacement battery for, say, a phone must be done in a shop.
Not realising this, I ordered a replacement battery via Amazon. It came via courier, in the usual Amazon way, and it carried a large warning label. It turns out Amazon have a special contract with the couriers.
Unfortunately, Amazon sent me the wrong battery. So I contacted them and they told me to send it back and they would sent the correct battery. They sent a Returns email which allowed me to print a large warning label for the return. I now know it is impossible to send a battery by post, and none of the courier services will touch it either. After exhaustive enquiries, I phoned Amazon. They knew of the problem and simply said 'Just dispose of it'. Fine; but when I tried to order another battery of the correct type they declined the sale.
You can buy them from eBay, via France, where they are advertised openly. How they can send it to you, I do not know, as I decided there are far too many fakes out there which don't have any significant capacity, so left it alone. I'm not fussed about a mobile phone most of the time, so I went back to my ancient £9 Nokia, whose battery still has life after umpty tumpty years. It' so old that the man in the local FONE shop just laughed when I asked for a replacement battery. How he gets his batteries is a mystery.
Marcus