I'm a big fan of the Eneloop rechargeable batteries. They have good capacity, durability, and don't develop a memory.
I'm also a big fan of LED headlamps. They provide decent light, are efficient, and free up your hands for other things.
One would think that rechargeable batteries and headlamps would go well together. They don't.
Here's the problem. Eneloop batteries come in packs of four and the charger is designed to charge them in groups of two. So far so good. The problem is that just about every LED headlamp uses three AAA batteries.
What do you do with the fourth battery? It just kinda hangs around waiting to get misplaced. Then it comes time to charge the other three, but the charger works in groups of two.
The only thing that works for me is to take 6 batteries. Use them in two headlamps. Wait for them all to be dead at the same time, then charge them up. Of course, then you have two headlamps out of commission until the batteries are all charged. Having 12 batteries would solve that problem.
This just gets out of hand. It's a small thing, and I might be getting a bit OCD about it, but there you go.