I have a Nitecore HC30 (a headlamp similar to the Zebralights) which is supposed to take 18650s, but it doesn’t work when I put in any of the NCR 18650Bs that I have. What’s going on here? Do I not have the right type of 18650? Is there anything I can do to make sure it does take the ones I have? I’ve been using the CR123A Lithium batteries that came with the light, and they’re working fine. Thanks for any help.
G'Day lgkiii, 
Are your 18650B's Flat top?
The Nitecore HC30 needs Button top cells, like virtually all other Nitecore lights.
This is due to Nitecore's reverse polarity protection.
Best Regards,
George
Solder blob on the positive side of your 18650 and you’re good !
Yeah, my batteries are flat top. OK, so I need button top. Thanks for the info.