Battery fitting issues with the Jetbeam BC40

Hey guys i have had a jet beam bc40 for over 1/2 a year now and recently got new 18650s to replace the uneven discharging cheap ultrafires I bought for it. So far i love this light, and the UF's have done well enough for what it is. The replacement batteries I got are tenergy button top 18650s. problem is, when i put them into the light, something felt off, and was tighter than usual to seat the tail cap compared to the UF 18650s. when i removed cap, i noticed an indentation in the negative terminal of the tenergy's, looks like the tail cap springs dug into it. I went on the measure the battery, and they are approx 1mm longer than the UF. My question is, anyone else encounter this problem? for reference the tenergy cell is a hair over 69mm long. light works fine, but i don't want to damage the batteries any further, and bottom out the springs. also the tailcap spring is much firmer than the spring at the head ( maybe the battery is just cheap and cannot take the compression?)

I've run into the same issue with my Eneloop AA batteries before and it hasn't seemed to cause any problems yet. But, NiMH cells aren't as touchy as Li-Ions.....

you'll be fine as long as the springs dont hit the protection circuit. bad thing about some protected cells is that the negative end is usually made of PCB material, which after wear and tear will eventually get worn out and contact issues will occur. There is however, some cells with a stainless steel boot, such is the 18650's of Fenix and some other brands which escape me at the moment.

Anyways, If you're worried about the spring eventually wrecking your cells, put the batteries in from the head portion, im sure the head of your 18650's more durable than its butt.

On my Crelant 7G5, i sometimes open it from the extension tube and put the 18650's on both halves of the light then screw it back on in the middle. Since the BC40's a solid tube, that is why i recommended opening it from the head portion.

I have a BC40 light that presses on the batteries. I found AW, Redilast, and Callie's Kustom seem to be stronger in the tail-end. My BC40 has old cheap batteries right now. There is a dent in the last battery. I've had no problems with it, however. On one light I put a thin magnet surrounded by an o-ring (for insulation) to strengthen the connection. That, too worked. Some springs can be ground with a diamond grinding wheel to flatten the part that touches the battery. I've used Tenergy batteries in many lights without problems.

thanks for the input guys, i added a picture for reference, also, would running flat tops ever work? or would need a thin magnetic spacer? also being a smart one i am i left a mark on both batteries

btw it it safe to run a flat top and a button top together? tenergy makes the same battery with a flat top

First post by this noob-flasholic. Just received my new JB-BC40 and inserted my brand new Panasonic NCR3400's. It would cut out constantly, always needing a bump/twist/roll to get in and out of Hi/Low beam. Quickly learned that not all 18650's are created in equal lengths. My NCR's are on the longer side measuring in at 69mm, so a pair of them are nearly 5mm longer than a "average" set. So when snugging down both the head and tailcap ends I was fully compressing both springs (and yes, the stiffer tailcap spring made the negative end of one battery convex). This told me that the ends were stopping (bottoming out on my longer batteries) before they could make good solid connection to the battery housing tube. This tube end needs to make an electrical connection against the ring inside the tailcap (make sure that ringnut is tightened counter clockwise with a pair of needle nose pliers). The other (head end) side of the tube needs to make electrical connection to ring on the head piece for Hi-beam. The design does not rely on the threads for connection but rather the very end surfaces of the tube. When you rotate the head counterclockwise to change to Low-beam, this breaks this connection then relying on the positive head-end spring-to-battery connection........ Long story short, if you suspect your batteries are too long you need to effectively make the tube longer. I simply bent a paperclip into a circle and dropped it into the tailcap so the tube, when screwed up tight, would press against it making a tight connection. All my intermittent light problems disappeared. Hope this helps.