I’ve done almost entirely away from AAA or AA batteries in my devices as have many others.

Having said that, you seem comfortable with a system that fits your situation. Cheers!

If I were doing much SAR work, I’d probably use a different strategy, but I’ve only been involved in a few serious rescues in 50 years or so.

The real-world situations I have most often experienced are having the headlamp turn on in my pack, my having failed to recharge it, and just having the lamp stop working (not a battery problem, but see below). You probably manage to avoid those situations, but I’ve experienced them all and expect to again.

The backup batteries I carry are lithium AAA cells, which have a very long shelf life, don’t weigh very much, work in the cold, and will power the lamp for a very long time. Also, they can be used in other devices, and it is easy to protect them from accidental discharge.

I also carry a key-chain light, one which takes one AAA cell, and is therefore one of the other devices my extra batteries fit.

Understood.

However, I do not find that to be needed for real-world use for most applications.

Now, a friend of mine is an ~20-year veteran of SAR, currently an officer in SAR, and owns a guiding company. He always said that the best backup for a headlamp batteries? Another charged headlamp.

In a critical situation where you may need a backup source, you don’t want to futz with batteries. Esp since in modern headlamps most of the weight is in the battery source and not the headlamp itself. Certainly more expensive than batteries, but much easier, efficient, and needed in literal life-and-death situations.

Note that cavers also mandate carrying three light sources and not batteries. (Hard to change in the dark!)

In other words, I find extra batteries a superfluous “belt and suspenders” approach for general camping and winter use. And those that need a backup for practical use vs. theory? They have a backup headlamp, as it makes more sense. (And in that vein, I have a small keychain light that’s good enough in an emergency, too: https://pmags.com/one-year-review-fenix-uc02)

Edit – And, of course, when camping my day pack or backpack has a separate headlamp, too