Also there are benefits to having a separate charger, as opposed to integrated charging. You can charge a battery while using the light, you have more control over how you charge your battery, the lights themselves are typically smaller in size, there is one less component in the light to break, and one less point moisture or dirt can enter. One of my favorite edc's is the zebralight sc64c le. It's a great quality light, and so small it's hard to tell how an 18650 can fit in there. It has a beautiful beam as well, that renders colors very nicely.
I'm also EDCing the exact some light (Zebralight SC64c LE). For me, it's just about the perfect EDC light. The thought of an SC600-one was mostly to get a bit more ooomph if only having one light.
You mentioned charging, which makes me want to mention that 18650s and similar are kind of a plattform you're buying into, that you can (if you want to) keep building on. Drop two cells in an XTAR PB2S-charger for example, and you have a combined power bank, where you can pull the cells for the flashlight if need be, and you just need a USB power source in order to charge (effectively charge either the power bank or the cells in it). Very nice.
Li-ion storage does result in loss. Storing a battery at higher temps (ie in car glove box in the summer) and with a higher state-of-charge (closer cell is to 4.2v) will result in more storage capacity loss. In other words, if you want to have the potentional for good capacity after a year on the shelf, store the light/battery in a cool place with 40% SoC (~3.8v).
This is true, you'll degrade the battery faster at higher temperature or SoCs, but in real world use, I haven't had much issues storing fully charged cells. For long term you're obviously right and I fully support it, but for practical use, I wouldn't worry about having a full cell in a light, or a couple of full cells ready to use. The difference hasn't been large enough that I've noticed it. A pile in a box though, sure.
