Okay, I'm tired of using search and not finding the answer to my question. I understand that Li rechargeable batteries are apparently particularly vulnerable to overcharge/over discharge and a few other quirks. I further understand that protected batteries do a good job at mitigating most of these risks. My question is what are the common denominators that apparently make some lights more susceptible to have a catastrophic type failure if theses occur....i.e. why is ABC light fine with unprotected rechargeables but "don't dare use" anything but protected in XYZ light. I figure there's a sticky on all this, but I couldn't find it. No problem, I've got a multitester and all my current rechargeables are the protected variety.