SureFire CR123 Negative Charge

tjswarbrick

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Mar 19, 2011
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691
Location
SF Bay Area, CA
Hi guys.
Something a bit odd just happened. I'm curious if anyone has had a similar experience, and can advise me how to keep it from happening again.
I acquired a SureFire G2Z with P60 incan head and SureFire CR123 batteries about 2 months ago. I've used it for all of about 20 minutes, but store it in my bag in the trunk of my car. Two nights ago, when I went to use it, it was dead. I replaced the batteries, and all is well again. However, when I tested the old batteries, one read 2.24V, the other -.65V (Yes, Negative .65 Volts.)
For your edification, I verified DMM polarity and tested both 3 times. I also tested the replacement Energizer batteries - both came out at 3.22V.
I hadn't locked out the tail, so it would be ready when I need it in a flash. There was nothing positioned above it, so I really don't think it was activated. But I suppose it's possible.
Luckily I had a couple other lights with me at the time, so I was able to find what I needed (Maratac AAA came through again.)
Since the one battery is reading negative, I'm wondering if it was old stock or defective.
With the new batteries, I've locked out the tailcap. As my emergency light, I really need it to be there when I need it.
Anyone ever see anything like this? Any suggestions to keep it from happening again?
Thanks for the help!
 

45/70

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Oct 9, 2005
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Location
Rural Ohio
Well, for starters, the fact that one cell was "reverse charged" is a strong indication that the light was activated when this occurred. From this I would say that you should definitely lock out the tailcap when storing your light, so as to avoid this happening again.

Also, the difference in remaining capacity of lithium primary cells that read zero Volts (or minus in your case) and 2.24 Volts is negligible, they are both "dead" cells. The open circuit (no load) voltage at which a CR123A cell is considered "dead" depends on the current draw of the application it is used in, but 2.24 Volts OC is "dead" by most any standard.

In the future I would, as I said before, utilize the lockout position to avoid this happening again. A light that you have to unlock the tailcap first before using, is more useful than one that doesn't work at all, in my opinion.

Dave
 
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45/70

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Joined
Oct 9, 2005
Messages
2,800
Location
Rural Ohio
I've just never heard of a battery switching polarity before.)

Hi tjs. 99.9% of the time when you come accross a cell with a negative voltage, it is because it has been reverse charged. This can happen when one, or more cells are used in series. In your example, one cell was drained to zero Volts before the other. In this situation the current from the "good" cell continued to flow through the "bad", or zero Volt cell. When current flows through a cell backwards from the normal direction, the cell is "reverse charged" and will result in the cell having a negative voltage.

Reverse charging is damaging to any type cell chemistry. With lithium primary cells however, it can result in a "vent with flame" incident, ie. an explosion. With cells that are well matched in capacity however, the potential for an exploding cell is reduced, as the energy level of all the cells involved is very low.

Dave
 
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