The last time I bought one, I selected a “Polaris V8” for using a removable 18650 battery. I wish that was more common.

• Runtime: infinite (just bring spares)
• Charge time: 10 seconds or so to swap the battery
• Service life due to the battery wearing out: infinite
• Service life due to being a janky no-name product: 3-4 years

So that last bit was disappointing.

Removable lithium batteries like 18650 or 21700 are not really a thing (except for a few hobbies) because they’re inherently dangerous and not a single respectable cell manufacturer sells them directly to end users (you can still buy them from unauthorized sellers though).

You can put your AA battery in the pocket with your keys and nothing scary will happen. Put there a 18650 cell and you might die from severe burns. So yeah, replaceable 18650 are awesome, but we’ll never see them because people are dumb AF.

Untrue. I use them for 10+ years for anything that’s possible (flashlights, powerbank and anything you can power with it) and they’re not dangerous if you follow SIMPLE rules. About as dangerous as a bottle of vinegar. And you can perfectly buy good cells for any application, Sony vtc5 or vtc6 are two examples, never buy cheap ones and NEVER buy from shady sellers. And btw: you shouldn’t put any battery to your keys in your pocket, that is called “stooo-pid” and makes little black holes in your thighs.