Both 16340 & 14500 are great cells, and I use both frequently. They're essentially ~the same thing in different form factor,
for most practical purposes. I also have several D25As, and several D25Cs, and use several of them daily. Keep in mind that there are protected 16340s with higher capacity than the Fenix cells you mention (which I've also used for years, but don't fit the D25Cs). Also keep in mind that both capacity and max current ratings should generally be considered together when choosing cells.
I do use a lot of 16340 lights, and prefer the form factor and performance capabilities of some of those lights to those of most 14500 lights. I also prefer having CR123A as my 'primary' backup source rather than AAs.
An example of a protected 16340 w/ 950mAh rating which I'm using is here, and these are my test results on 4 samples. They were tested at 2 discharge current rates, to a discharge cutoff voltage of 2.8V (the manufacturer likely uses 2.5V). (They also fit nicely in a D25C):
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.....About a week later, I tested 4
new examples of NL-169, a newer version Nitecore protected 16340 cell with a rated capacity of 950 mAh using the MC3000, with same parameters as previous tests. I paid unit price of $6.95USD for these cells.
photo.nitecore.com
Those results were:
Cell #1 - 905 mAh - 0.153Ω
Cell #2 - 913 mAh - 0.158Ω
Cell #3 - 911 mAh - 0.161Ω
Cell #4 - 897 mAh - 0.165Ω
I re-ran the test on the same 4 cells, but this time I used a discharge current / rate of 0.5 A (rather than 1.0A used in all the previous tests) with these results:
Cell #1 - 925 mAh
Cell #2 - 938 mAh
Cell #3 - 940 mAh
Cell #4 - 924 mAh
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That info is copied from this post:
During the course of doing some cell testing in the past few weeks, plus the initial checkout of a new 'charger/analyzer' I acquired, some data from my notes may be of interest to some, so I'll share it: The 2 devices in use were: Opus BT-C3100 V2.2 SkyRC MC3000 FW EDIT: Rev:1.15 NOTE...
www.candlepowerforums.com
If you're interested, here are some protected 14500s I'm using which test well and fit nicely in a D25A:
The NITECORE NL1475R is a 750mAh 14500 micro-USB rechargeable battery that's compatible with multiple 14500 flashlights, headlamps and other electronic powered devices. No charger is needed to recharge this battery, it's equipped with a built-in micro-USB port that allows users to charge the...
www.nitecorestore.com