Has anyone actually run into problems with the generic 18650 batteries sold on eBay? Do they really have shorter life (whether it's how long a full charge lasts, or the entire lifespan)? Theoretically they may risk hazard like explosion, but I assume very rarely? Also many of them claim to have protection circuit, which I doubt, but I still buy them. They are dirt cheap in comparison, so maybe that make up for the shorter life (which is still pretty long).
Where do you think the 18650 batteries came from in all those cheap Amazon no-name hoverboards that started fires? The brand name batteries cost more than the nonames. But they last for years so the incremental cost is pennies a day, maybe. It's hard enough to get it right with brand name batteries. Ask Samsung and Apple!