In reply to James Gordon:
Goodness me, don't people improvise any more?
Use whichever head torch you like most and suits you best.
* If it's not cold use standard rechargeable, the Panasonic Enloop pro are a bit more pricey but good quality and should be good for more charging cycles than standard rechargeable
* If it's a bit cold, like freezing or a bit below, the petzl core batteries are noticeably better than standard rechargeable.
* If you need to go somewhere genuinely cold. Improvise, make yourself a wooden "battery" from a bit of dowel and drill a hole through (longitudinally) and another in the middle from outside (laterally) halfway - to join with the longitudinal hole. Solder some metal end caps to wire and thread it so the wire comes out of the middle.
Attached is a pic of a shockingly bad example that's a hasty bodge, with a bit of time you should be able to make a much better job than my pic, also it's AA size and you probably want AAA for most head torches and you want a much longer wire than this picture. Genuine Petzl part, honest! 🤣
Make one or more additional wooden"batteries" that just connect the two end caps together (if you need to fill up other battery positions in series)
Now you can run your torch from an external battery holder that you keep inside your jacket. This will cost you some wire, a couple of blobs of solder, small bit of wood (or two/three). Problem solved.
Post edited at 15:38