Which is the culprit---the light, the batteries, or the battery tester?

Eagletac P20C2 MK II with XM-L HO module with 2 new Panasonic CR123 batteries installed on the same day, and both tested at 100% capacity with the ZTS tester---after using the light at MAX and General and Lo output for seven to ten days for a short duration each time and testing the batteries today with the ZTS tester, one battery consistently showed a remaining capacity of 20%, and the other battery consistently showed a remaining capacity of 100%. I tested the batteries over and over for many rounds, and each time the result was the same.

My question: Which is the culprit---the light, the batteries, or the battery tester?

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lovemylexicon said:

Where did my post go?

Can't find it anywhere!

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You posted it in LED Flashlights. I'm going to move it to the Batteries section when I've finished this reply.

The ZTS is only accurate to ~25% at best. It's better than nothing, but there is no method of testing that is as accurate an indicator for primaries as cell voltage is for Li-Ion cells.

If one cell is now showing 20% and the other 100%, you should probably stop using them together.

I'll leave others to comment on the electronics/performance of the light itself.

Really hope someone can shed some light on the cause!

Anyone?

Hello Lovemylexicon,

I think it is time to run another test. Take a new set of cells and subject them to the same process. Pay attention to which cell is in what position. Let us know what you find out.

Tom

I did that, and the same thing happened.

The top cell reduced to 20 to 40 percent capacity, while the bottom cell remained at 80 to 100 percent capacity.

The XM-L drop-in was purchased separately. The light originally came with an XP-G R5 LED module. I think the problem is caused by the XM-L drop-in, but I don't know what is the cause.

I presently have no access to the original module to do the same experiment

Can anyone provide any information based on the above information?

Hello Lovemylexicon,

Interesting...

This has been observed many times before, but it is not known how it can happen.

The theory is that the cell that is nearest the light warms up more than the other cell, and this increased temperature effects the chemicals inside the cell. The problem is that some people observe exactly the opposite. The cell near the tail cap is the one that discharges first.

The next step is to run the light just to the point where it dims. You want to watch this closely and not run it beyond the point where it dims, but you want to run it long enough to have the lower output noticeable. After that pull the cells and let them rest for 30 minutes, then check them.

Tom