Using 2 18650 batteries in place of a 4 cell pack ?

I have 2 lights and I would like to use light1 with the battery container of light 2.

Light 1
light = 3x Cree XM-L T6
battery = 4x 18650 battery pack (stated voltage on website says 8.4v) 4400mah
mount = handlebar

Light 2
light = 2x Cree XM-L T6
battery = battery container for 2 18650 . I am using 2x Enerpower 3400mah 18650.
mount = headlamp


I have attached light1 to the headlamp mount of light 2 which works well. I would like to use the 2x battery container to power it. Is this possible? I was going to simply going to cut the battery cable of light 2 and place a power connecter in (to match the light1 connector) so it can be used with either light. The problem I see is that the battery container on light 2 seems to be wired in parallel (see pic below) which I think means its only producing 4.2v not 8.4v . I'm not sure why 2x cree are fine with 4.2v and 3x need 8.4v.


Is this possible? Have I made any incorrect assumptions? pics below :


light1 is at the top of the pic light2 at the bottom (on the left is another light I am cannibalising for the mount and battery container, but they are the same as light 2).




if image links are dead here are 2 new ones
http://s12.postimg.org/teweidrkd/IMG_0931.jpg
http://s10.postimg.org/sobt2tk1l/IMG_0932.jpg

The short answer is that it's not going to work.

Different lights need different voltages, depending on how the LEDs are driven. For example, a light using a constant current buck driver typically requires an input voltage that is at least 1V or so more than the output voltage, but can usually cope with significantly more.

I'm guessing that the two 18650s in parallel are being used to drive two LEDs in parallel directly.

Unless your battery packs are both outputting about 8.4v (max) with the 2 cell in series and the 4 cells in series/parallel it probably won't work. I am guessing pack 1 (4 cells) is a 16.8v pack with the 3 LEDs in series with a buck circuit that would equate about 12v when the cells are depleted which makes it easy to drive the 3 LEDs in series all the way to nothing. The 2 cell pack is probably 8.4v.

The 2 cell pack is probably 8.4v.

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Did you look at the photos? The 2 cell pack looks a lot like it's wired in parallel, as the OP said.

pdw said:

Did you look at the photos? The 2 cell pack looks a lot like it's wired in parallel, as the OP said.

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I can't tell from the pictures. If the pack has a charging solution built in it would have a way to both charge in parallel and operate in series somehow too.

I can see a wire marked "+" going to one end of the pack (to what looks very much like a single plate joining the two terminals) and a single wire marked "-" going to the other end. There are no other wires going to the batteries. I can't see how that could operate in series.

pdw said:

I can see a wire marked "+" going to one end of the pack (to what looks very much like a single plate joining the two terminals) and a single wire marked "-" going to the other end. There are no other wires going to the batteries. I can't see how that could operate in series.

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I only see a single battery holder and there is a lot more than 2 wires on the board in the second picture. If it was all in parallel you would only need two wires in and two wires in out not 6 or so wires

The only wires connected to the cells are two of the white wires. There is another pair of white wires going to the charge socket (the dongle at the bottom of the picture) and then three wires (red, blue and clear) going to the LED and switch. I can't see how the cells can be anything but wired in parallel.

pdw said:

The only wires connected to the cells are two of the white wires. There is another pair of white wires going to the charge socket (the dongle at the bottom of the picture) and then three wires (red, blue and clear) going to the LED and switch. I can't see how the cells can be anything but wired in parallel.

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If they are wired in parallel it would be easy to test that just insert one cell and see if it works. Regardless of it all I seriously doubt the 4 cell one has all in parallel too.

Lynx_Arc said:

If they are wired in parallel it would be easy to test that just insert one cell and see if it works. Regardless of it all I seriously doubt the 4 cell one has all in parallel too.

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Just tested it. It does work with only one cell in there.

It seems I may have to use the battery pack that comes with the 3x Cree LED light and just be really careful. Was hoping to use my nice safe german Enerpower batteries.