2 or more batteries in series in a metal tube flashlight = shortcircuit danger?

[Napalm]

Guys, think for a second a 2xAA, metal tube construction. Something like a Maglite Mini AA. I just inspected my rechargeable NiMh AA batteries and found a couple of them with damaged insulator around the body (especially around the (-) end) - this comes from repeated insertion/extraction from all kind of carriers, including the one in the charger. And the plastic shirt on the batteries gets chipped/cut on that end quite easily with some brands (as the material is rather thin and frail).

Now if I insert such damaged battery in the head end of a 2xAA metal flashlight, and its casing makes contact with the metal body through such insulation defect, it will definitely short-circuit the battery installed at the tail end (which by design is connected with the (-) to the flashlight body and with the (+) to the external casing of the next battery, which now connects to the body too). So the tail end battery will either leak (alkalines), overheat (NiMh) or even explode (Li).

My question is - given that the insulation on the body of the batteries is not stellar these days - why don't flashlight manufacturers insert a plastic tube inside the metal tube, to make sure that in case you use a battery with damaged insulation, you don't short-circuit the other batteries installed in series with it?

Or, if some manufacturer actually does it, can you guys recommend it?

Nap.

 

[Lynx_Arc]

most metal bodied flashlights are at least cheaply anodized which insulates them from conduction well. If you do get a short on the case of a cell on a maglite it will have to be the first (top cell in order to be a problem and typically the anodizing there is less damaged than the one at the bottom.
Another thing is... I typically don't put batteries in a light blindfolded so it is rather obvious if a battery has a damaged cover. I can take a piece of clear scotch tape and tape over the cell to cover the problem and I am good to go.
The one reason they don't use sleeves is it would cost more, the sleeve would become damaged causing the cells to jam up and the light would have to be a larger diameter to accomodate the sleeve.

 

[Napalm]

Mhhh I pulled out the multimeter and indeed the tubes on my lights are anodized inside and the anodizing seems to be non-conductive. But since that thin anodized layer could become damaged by wear/scratches, I also pulled out a "Scotch Super 33+ Vinyl Electrical Tape" roll to fix the suspicious looking batteries. Worked fine with other lights but not with the Maglite Mini - the tube on this one is a very tight fit, and as soon as I add some tape on the batteries they won't fit inside. Guess I'll just have to carefully inspect batteries when replacing.

May I assume that the 1 cell flashlights are inherently safer? or if you have something like a light that can take either 2xCR123 or 1x18650, it is safer to use the later?

I also looked at the "exploding Pelican" thread and noticed that the Pelican is *not* anodized inside, and in one experiment with a 60% capacity battery in front and a 100% one in tail, it is the 100% one that blew, although the "reverse charging" theory would have said that it is the 60% that should have done that instead. But the position of the batteries suggests that the 100% one could have been short circuited if the other battery had a damaged insulating cover.

So guys. Be careful. Inspect the plastic coat on your batteries before inserting them in series in a metal tube.

Nap. :candle:

 

[Lynx_Arc]

electrical tape is a lot thicker than magic mending tape (clear) that I use on cells. If the cell still won't fit you could try a little clear fingernail polish. Most light designs use the tube to complete the ground circuit. The only two problems you could encounter is a light with a tail switch off coming on if the cell farthest from the light engine shorts to ground or the lower cell being shorted out if the cell closest to the light engine shorts to ground. If the light has a tail switch and it is off it should not do anything till turned on them the short will have a completed circuit to drain the bottom cell quickly overheating etc it with consequences. If the light is a twisty then the shorted bottom cell (via the damaged top one) will heat up when the tail cap is screwed on to complete the tube ground circuit. My advice is if you have damaged cells put the damaged one at the bottom at worst when you turn the light on nothing will happen and things will heat up but it will only do so when you activate the light not when you put the tailcap on (if the tailcap switch was off).

 

[Napalm]

I'm thinking about something radical. Peel of the existing (damaged) plastic coat from the batteries and replace it with heat shrink tubing.

Call me crazy but I have plenty of new batteries that went through only 3-4 recharge cycles but have the insulator damaged around the (-) end because of some stiff spring in a carrier.

So anyone already did this? Any advice? Dangerous? (I'm thinking NiMh AA).

Nap.

 

[Slickseth]

I believe you will find exactly what you need here:

http://www.batteryspace.com/pvc78inch25mmwidthshrinkwrap1lfordiybatterypacks.aspx

 

[Lynx_Arc]

I'm thinking about something radical. Peel of the existing (damaged) plastic coat from the batteries and replace it with heat shrink tubing.

Call me crazy but I have plenty of new batteries that went through only 3-4 recharge cycles but have the insulator damaged around the (-) end because of some stiff spring in a carrier.

So anyone already did this? Any advice? Dangerous? (I'm thinking NiMh AA).

Nap.

should be ok if you find the right thickness of heat shrink. If it is thicker you may find your batteries not fitting well in some devices though. years back when I was poor and nimh batteries cost $15-$20/4 pack I bought battery packs on clearance and stripped the cells from them soldering tips on the ends and in the process some of the packs were glued together so I had to cut batteries apart and I just used scotch magic mending tape over the bad spots. It is very tough and thin and has lasted longer than the batteries have even charged on a 1 hour charger mostly. Being clear you don't lose what the label says either.

 

[EngrPaul]

I cut a sheet of thin mylar (or similar) as long as the flashlight tube and length matching the circumference of the inside of the tube. Roll it up, slide it in. It self-retains, especially if you cut it exactly the right size that the seams butt against each other. Paper works in a pinch but I prefer something that holds up over a long period of time.

This is also beneficial if you need to use magnets between cells for any reason.

 

[Lynx_Arc]

I cut a sheet of thin mylar (or similar) as long as the flashlight tube and length matching the circumference of the inside of the tube. Roll it up, slide it in. It self-retains, especially if you cut it exactly the right size that the seams butt against each other. Paper works in a pinch but I prefer something that holds up over a long period of time.

you could also just roll up your batteries in paper or something before you stick them into the light if there was enough space for it.