Surefire/3V Battery Failure Question

[Safetyhit]

Is it normal for a Surefire to go from working fine to not working at all as a result of battery weakness. No dim or weak projection prior, just from seemingly fine to completely out?

I have one that takes 3 lithium batteries that recently died. When I tested the "old" batteries they came up as still being in the green (adequate power). But, since I had 2 new batteries around, I thought I would try a temporary swap of two of the old ones just to see if maybe it was the bulb that had died.

The light functioned again. However, it had a very short life, maybe a total of 30 seconds (in small increments) before it would not work yet again. The batteries still show adequate power, but somewhat diminished.

I know using one old battery with two new ones is not a great idea, but it was for such a short time that I can't figure what the hell is going on. Should I just get all all new batteries at this point? The other 3 still show sufficient charge, but I am guessing that maybe if they slip beneath a certain threshold they can't power the light regardless.

[Byron]

Can you provide some more detail?

LED or incan? What SF model? What method did you use to test the batteries that you found them to be 'in the green'?

[Safetyhit]

Can you provide some more detail?

LED or incan? What SF model? What method did you use to test the batteries that you found them to be 'in the green'?

Certainly.

It is a Surefire M961XM07. The battery tester is one I purchased at a hardware store with settings for nearly every type of battery made. There is a slight difference between the new and old battery readings, but the old ones are still well in the green (good) zone. Most household batteries fail when they are on the red/green line.

I was reading in the manual (that I finally recovered) that one should "never" use new and old batteries. But it was for just seconds, not nearly even a minute. Still, I am just going to get a new box of 12 from someone. Will see what Grant has.

If you think it may be something else Byron, I am all ears. Hate to waste 3 good lithiums for nothing. Appreciate the assistance.

[theJanitor]

incan models normally go dimmer as the voltage drops. the LED's normally maintain a constant level of output until the voltage drops below a certain threshold, then there may, or not, be a lower output level that runs with the lower voltage.

i've seen this on all of my surefire lights, except for the x300, which i haven't run till the batteries got that low.

Safetyhit, do you have another light that you can try these batteries out on? I can't see the incan bulb shorting out the batts, but you never know. if you need a bulb to try these out on, i think i have a couple spares for the 961. pm me and i'll send one out to you

[Byron]

OK, good info. Far from anything authoritative, but here's my scientific-wild-ass-guess with some points. I fully concede that I could be way off here.

First, theJanitor is correct: in general incans will slowly dim over time. Modern LED lights tend to be regulated for a flat discharge with rapid dimming near the end (I'm painting with a broad brush here, as there are many differing examples). So that said, your light should have dimmed over time, but given the way our eyes perceive light I wouldn't rule it out of the equation that it's been dimming a while and you didn't fully notice.

That's not to say you're an idiot or anything, it's just that we don't see brightness in a linear way, so a linear decrease in brightness is hard for us to perceive when it's spread over time. I have had plenty of times on my old unregulated lights where I thought it was performing well and then swapped out batteries to be met with a "holy crap" effect of returning brightness.

That's my long way of saying that my guess is that your batteries are simply too dead for that light. They will probably still work in low drain devices, but I wouldn't use them together. For example, a red Inova X5 would be great for feeding those dead batteries to. It's a real battery vampire.

Anyway, I'm rambling. Most store-bought battery testers do not place much (if any) load on batteries during testing: they just test resting voltage. For a lithium battery this can give a false reading of the battery being green since lithiums do not experience much voltage sag until they are under load. A practically dead lithium primary won't look significantly different in voltage compared to a fresh one if tested without load. Something like the ZTS, which tests with a pulse-load, is required for accurate testing of lithiums.

Your light has a 60 minute runtime according to specs. Do you think you've put that much burn time on it?

I think you're really just best off putting in an entire fresh set of batteries and relegating those used ones to either the recycling bin or to battery vampire devices.

And I know that you already know not to mix batteries because it's not good for the device, but in case you didn't also know, it's not just a device issue. There's a safety issue: http://flashlightreviews.com/features/123burst.htm

Also note in that link that factory cells can come in various states of charge. It could be that even if you didn't but much burn time on that set, one of the batteries or more wasn't great from the factory.

Like I said, most of what I say is speculation, but your situation doesn't sound abnormal to me (for whatever that's worth).

[UVvis]

How does your battery tester work?

Most 123A sized lithium cells will hold their voltage, but have no capacity. A voltage only test will still have them at 2.9-3.3V when they are dead.

If you are using a pulse load tester, you get a more accurate measure of the battery's remaining capacity.

With an incandescent bulb, it is normal for the light to just die. Maybe you will notice a slight dimming beforehand.

Also, the reason why with lithium it's bad to mix new/old cells, is that there is a serious risk of the dead cell bursting and trashing your light. This usually only happens with high draw multi cell incandescent bulbs. I've had this happen twice.

With two new, and one dead cell, the two batteries are going to try to reverse charge the dead cell. With lithium primaries, this is bad as they aren't made for it, and they just get really hot.

[Safetyhit]

That's my long way of saying that my guess is that your batteries are simply too dead for that light. They will probably still work in low drain devices, but I wouldn't use them together.

I agree this is probably the issue. It's the first battery change for this particular light, but it is not the only Surefire I own. I have 3 in fact, but this was the first time I dealt with this seemingly abrupt loss of power.

Not sure what to say about the battery tester other than it has a voltage setting dial and a red and black wire to hold against the battery ends. Has worked well for years.

Thank-you for all the helpful replies. I am just going to use this as an excuse to get a new pack of batteries. If that doesn't help, I know I have a bigger issue and will change the bulb.