SAFE BATTERY STORAGE IN MULTI-CELL LIGHTS

I have read the sticky about the two cell light that "rapidly disassembled" and I have some questions.

I am assuming that these cells ignited because one cell had a different level of energy than the other. Why did the batteries ignite only after the light was turned on?

I remember reading some time ago about a woman who placed a Surefire 6P in her purse and put the purse on the bed. Shortly, the purse was on fire, apparently caused by the batteries in the flashlight. In that case, the light was not turned on and spontaneously ignited. Why would that happen?

Once someone can explain why cells ignite when one has less energy than the other, then I would like to know whether batteries can safely be stored in lights. It's bad enough to have two cell lights, but I have a number of 4,6 and 8 cell lights. Would it be sufficient to loosen the tail caps, or is the danger still present with the batteries installed in the holders?

Bill

Hello Bill,

In a multicell series battery if one cell goes empty the other cell(s) will continue to push current through that cell. This results in a reverse polarity situation. When this happens internal pressures and temperatures build up.

If the temperature is rapidly increasing shutting the light off may not be enough to prevent the internal temperature of the cell reaching its critical level. This is hard for me to understand because the performance of the flashlight should drop off drastically before you get to this point, but it is a possibility.

Another possibility is that the light goes out and the light is not shut off. This allows the circuit to remain intact and if the imbalance between the cells is high enough it can force the pressure and temperature to continue to climb.

The safest way to store a multicell light is to remove the cells from the light and check them to see if any of the cell are hot. Unfortunately that is not very practical.

The next best way is to unscrew the tail cap to make sure that the circuit is broken.

In addition, be mindful of the performance of your light. If it flickers are shows signs of running out of power, shut it off and remove the cells.

When using primary cells it is best to have another light that runs on 1 cell. You can use most of the capacity of the cells in your multicell light but before they are completely empty you can remove them and use them in your 1 cell light to get the last little bit out of them.

I know some people that feel that the best way to be safe is to use their lights for an evening or two, then replace the cells with new cells. They fully understand that they are recycling cells with some capacity left in them, but over the years they have never had an issue with the batteries. I picked up a ZTS tester and use that to monitor how well the cells are matched.

Tom

Hi Tom,

Thanks for the great explanation.

One more question. Is there any difference between a battery holder that is in series and one that is parallel or series-parallel? I vaguely remember reading somewhere that the parallel or series-parallel holders could cook off even out of the light, or with the tail cap unscrewed. Is that right? If it is, then it would do no good to loosen the tail cap of a parallel or series parallel light set up.

Bill

Hello Bill,

There is no problem with parallel set ups. In parallel when the cells die everything shuts down and there is no opportunity for attempting reverse polarity.

Series set ups are where the problems can occur. A series and parallel set up is also a problem because of the series component.

IF your holder is disconnected from the circuit and IF none of the cells are hot when you stop using the light, they will not cook off.

If you stick to quality cells there are very few problems that come up. The main problem is when you go to load up the holder and just grab whatever is laying around. This has caused a lot of problems because even though you took all the cells out of a similar holder, they may not all be discharged to the same amount. The rule is once you take the cells out replace with new unless you have something like the ZTS tester to check them first.

Tom

Thanks again Tom. Seems like the ZTS tester is an important piece of equipment.

Bill

Is the issue of one cell becoming discharged too soon an issue for both primary and secondary cells? If all the cells are protected secondary cells, is that still an issue? Thank you

Hello BrightLight,

The issue is that one cell starts off at less of a full charge than the others. As the battery pack discharges, this weak cell is drained before the others and the other cells push current through the cell. This kind of acts like reverse charging the weak cell and it heats up.

Secondary cells with protection circuits should not be a problem IF the protection circuit functions properly.

Tom