Lots of laser pointers and even LED flashlights from Walmart support 18650s (they also have a 'cartridge' that can use 3 AAA batteries in place of the 18650).
However, the 18650s have no internal electronics to prevent any charging mishaps.
That is a good point. What's a good LiPo protection circuit look like? Some googling led me to some basics that a protection circuit should have, does this look about right?
- Overcharge protection (prevent charging past the max voltage, probably ~4.2V but intentionally shrinking this window might prolong cell life)
- Short circuit protection (Like, a fuse? Would a PTC one work?)
- Limit charge current (0.5-1C for LiPos, 5-10C for LiCaps, etc)
- Undercharge protection; prevent discharge past a 'low voltage' value and (ideally) permanently disable cell or severely limit charge rate if voltage drops below the minimum safe value.
- (Ideally) Balance voltage between individual cells.
However, the 18650s have no internal electronics to prevent any charging mishaps.