They do but it's fine in some situations. Surefire is a tactical company. They want their lights to always work. It's why they still make them for primaries. They're more reliable. But if you can get the voltage close enough, most will work. But not for incandescents. Not these cells anyway. Just 3 primary cells lights work with 2 regular lithium ions. Because the voltage works out to being the same for their LOLAs.I think SF admonished not to use rechargeable batteries with their incandescents, didn't they?