A HUGE issue in the area of dive lights is the almost exclusive focus on the LIGHT. The light is garbage without a GOOD battery. The battery will soon be garbage without a good charger. And the whole package is kind of tenuous and potentially dangerous if the operator doesn't understand the basic principals, use, care, and what constitutes abuse of all 3 components, especially the charger and battery.
Ignorance about batteries and chargers is a significant and pervasive problem. Purchasing of crap components is common. Devious/deceptive marketing on the net, eBay, and China is rampant. Sucking in uninformed purchasers is dead easy. In fact, they are often SO uninformed they think they got a really good deal. It IS hard to sort out the decent from the junk. I've seen junk batteries being sold on line by mainstream reputable dealers. I'm sure they thought they were doing their customers a service. Often the working staff is poorly informed.
THAT is the real recipe for disaster, NOT Li-on batteries and chargers by themselves.