NCR18650B cells unreliable

I've been trying to troubleshoot a problem, but I think I have narrowed it down to the batteries, so I'm posting in this thread for some help.

Based on the review published here at CPF, I purchased a Jetbeam BC-40 in late 2012, and I also picked up an intellicharger i4 charger, and a couple of NiteCore 2300 mAh 18650 batteries.

This combo has worked well as a bicycle headlight, though I needed higher capacity batteries for longer ride times, so I picked up some Made in Japan 3400 mAh 18650B cells from r-l sales. I've also used these cells in a homemade sled to power my taillight (DesignShine DS-500).

Here's the problem.
Late in 2015, I purchased some additional Made in Japan 3400 mAh 18650B cells from GearBest. These seemed to be fine, though I only rarely used them when my other cells were in need of charging.

I eventually soldered up a 4-cell battery sled (2S2P), and it worked fine to power my taillight using the GB cells during a 4-hour test run in my living room. Unfortunately, the taillight stopped working during my second ride while using the 4-cell sled with the GB cells. I found that jostling the battery pack can interrupt the circuit, but I inspected all of the solder joints and they were good.

In trying to troubleshoot, I tried the same GB cells in the Jetbeam, and gave it some hard bumps with my hand to simulate hitting a rough patch of pavement; the light would flicker or quit almost every time. When I removed the cells I noticed that the negative contact on both cells was now concave after tightening the end cap all the way. The r-l sourced cells have never flickered during a ride.

Are the GB cells possibly defective? Apologies if this is this a known issue that has been discussed here previously.

The GB cells work fine unless they are jostled in a flashlight or sled, so I don't trust them for use on a bicycle or being handled roughly. Do I write these off for on-road use?

L-R: GB cells 1-4, r-l cells 5-6
Cell 3 with concave negative contact


Cells lined up next to 2-cell sleds I purchased awhile back. This style has worked fine for years, though the contacts are exposed and need to be covered with tape.



L-R: GB cells 1-2, r-l cells 3-4

There are two purely mechanical issues:

1. The wider the contact surface the easier to crush it;
2. If you do not use springs or cushions of any sort your batteries will be crushed with almost 100% probability.

If your batteries do not "float" on springs or cushions you have to attach them in such a way that only external perimeter on the edges of the cylinder (the strongest part) would accept mechanical pressure, not fragile contact surfaces.

Your cells are of the "protected" type, which is very advisable in multi-cell flashlights like the BC40. This means they have an additional electronics module in the small black disc at the end (see https://lygte-info.dk/info/isMyBatteryProtected UK.html for lots of pictures and a short explanation). You can see that this additional stuff looks different in the GB vs the r-l cells on your first picture.

You might have broken some electrical connections in the protection electronics by forcing the GB batteries into that battery carrier. I have some cells here that look identical to your GB cells in every way (that I bought cheap from some chinese dealer) and, while performing very well, they are rather long. All of mine are slightly dented as well because they are a tight fit in many flashlights.

Helmut.G said:

Your cells are of the "protected" type, which is very advisable in multi-cell flashlights like the BC40. This means they have an additional electronics module in the small black disc at the end (see https://lygte-info.dk/info/isMyBatteryProtected UK.html for lots of pictures and a short explanation). You can see that this additional stuff looks different in the GB vs the r-l cells on your first picture.

You might have broken some electrical connections in the protection electronics by forcing the GB batteries into that battery carrier. I have some cells here that look identical to your GB cells in every way (that I bought cheap from some chinese dealer) and, while performing very well, they are rather long. All of mine are slightly dented as well because they are a tight fit in many flashlights.

Click to expand...

To clarify a bit, the dented cells were inserted into the flashlight, not the Keystone 1048 sled.

Here is a picture of the BC-40 and DIY mount. The tailcap has a standard spring contact.



Here is the 2S2P holder.



Although I tried using 4 r-l cells, I was still able to interrupt the circuit by bumping the top of the holder, but not the bottom or sides. I wonder if the cells are losing contact at the bottom of the holder since there are no springs there? It may not actually be a battery issue after all. I may try to use a couple of 1048 sleds instead.

Can anyone recommend a 4-cell sled that will fit the longer (69mm) protected cells? It's been awhile since I searched. Thanks.