Sofirn SP35 popped 21700's fuse/CID in jacket pocket. Design flaw?


Newly Enlightened
Dec 5, 2008
I have an SP35 SF22Bxxxxx. Last I've seen it, I put it in my jacket pocket. When I tried to turn it on, it doesn't come on.
The rechargeable 21700 reads 0.0v. It won't take any charge in the light, or with external power supply.

I followed the video below and the cell was revived. After the revival, it still had plenty of charge left at 3.8v. I am thinking it accidentally got turned on in the pocket and the light got hot enough to heat soak the battery to the point of popping the CID. The placement of button on the SP35 is such that its really easy to accidentally activate in the pocket too.

Isn't it design flaw?
to have a combination of a
1.) switch that is so easy to be accidentally activated into high mode
2.) remains powered on and allows itself to get hot enough to the point of popping the safety switch on battery.

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Flashlight Enthusiast
Mar 31, 2015
since you experienced that the Unlocked light can turn on in your pocket (accidental discharge), you should read the manual and learn how to use Lockout..

here is a review that includes a copy of the manual, if you find the paper manual print too small to read

when a battery reads 0 Volts it is because the Protection circuit was tripped.. Some chargers can reset the protection.. However, according to that review, the stock battery that comes w that light is UnProtected and looks like this:

Did you use some other battery than the one that came with the light?.. Some lights are not compatible with Protected batteries, the light output can be too high, and can trip the protection, as you seem to have experienced.

That video you linked shows some potentially very dangerous use of metal tools that could cause a Short Circuit.. Im glad nothing catastrophic happened to you. IF you are using a Protected Battery, it will probably trip again during high output use..

I strongly advise you to only use the Stock UnProtected Battery, and use Lockout when the light is in a pocket.

I would not say it is a design flaw that you failed to use Lockout.. imo it is user error, for failing to read the manual, and follow instructions on how to use Lockout, in order to prevent accidental discharge.

another way to lock the light out, so the switch is disabled, is to unscrew the head or the tail half a turn, so the switch button will not work accidentally in your pocket

Im glad your accidental discharge did not burn a hole in your pocket, nor burn your body..

Definitely do NOT carry that light unlocked, now that you know that the button can get pressed accidentally..
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