My take on the protection circuits is that as long as you don’t do anything silly they’re largely unnecessary. Is that fair? They seem to just protect against overcharging, short circuits and excessive heat, all of which can be avoid by just not being an idiot.
In my somewhat experienced opinion, protected cells are only prudent with ‘series’ lights and the noobs.
I have a few protected cells, but I was a noob once.
For anything Lithium-Ion, never cheap out,.
Buy Lite beer, Happy Meals, or cheap toilet paper, if you have to save a buck.
Chris
The only reason I would still use a protected cell is that it would have a built in USB charging port which is handy for travel.
If performance is what you are after, unprotected is the way to go for price, max capacity, max current draw, etc.
Using unprotected batteries in a cheap poorly made light can be dangerous, as it can over discharge the battery.
If you are asking about which are the best batteries, I assume you aren’t using cheap flashlights 
Thanks for all the replies. I’m going to order a couple of Sanyo NCR18650GA and see if they are noticeably better than the panasonics I have.
Panasonic and 3400mAh usually means NCR18650B, they are usually quoted as 4.9A (1.5C) or 6.7A (2C), I don’t know how they got 17A (5C), that number looks arbitrary.
BTW Panasonic and Sanyo actually are the same company.
Postage from nkon.nl to the uk is long and expensive at the moment so I ordered a couple of these instead: https://www.18650.uk/lg-mj1-18650-battery-button-top
probably not a huge difference
https://lygte-info.dk/review/batteries2012/Common18650comparator.php
Below 5 amps, they appear nearly identical. Above 5 amps through to 10, the 18650GA is better.
Well the LED in my light only pulls 5A max and probably a lot less when thermal regulation kicks in. The 18560Bs I have are probably fine really but I guess if your load is (maybe) 5A then having 10A load capacity is better than being right on the edge.
The battery comparison (well that entire site) is great for finding out useful info.
e.g Sanyo GA 3500mAh vs Samsung 30Q 3000mAh
At 5 amp the Samsung out performs the Sanyo right up until the end. Meaning you’ll get more light for longer from the lower capacity Samsung. Right at the end the Sanyo will keep going longer, but at a much reduced output for the final bit.
I didn’t grab a screenshot at 3amps, they are a lot closer here. With a longer low output run for the Sanyo at the end. But at 3amps the real world performance would be very similar.
If you mostly use low modes, the Sanyo will offer better runtimes. Down at sub 3 amps or even 1 amp you’ll get noticeable longer runtimes. But if you mostly use higher outputs 3amp or above. The Samsung will probably give you better runtimes before you want to recharge.
That graph is set to 5A and that’s a lot of light and heat, seeing that the XM-L/L2 pull about 3 amps at 1000+LM.
Set the graph to 2A and see what you see?
Chris
Just for shits and giggles I’m going to run my light with one of these NX batteries until it goes out and then stick it in the XTAR and see how much current goes back into it.
About 60% of ALL my Li-Ion cell’s are Samsung 30Q.
I’m not gonna change that because there is a new kid on the block with 1 extra mAh.
Have a few light’s with multiple batteries in series. For that I use my older protected Keeppower’s.
Mainly because they were the go-to batteries at the time of my more “precautious” period.
My other protected batteries went into lights I gave away to (serious) muggles.
I NEVER give a light with a Li-Ion battey to someone who’s only focussed on the WOW thing.
The panasonic NXs are still going strong at 2h in so can’t be too far off their rated capacity.
Just be aware high selfdischarge 30Q can have sometime. Developing gradually with time.
Here is comparison of familiar cells :
2h 20min, popped it out quickly and tested voltage - 3.28v. Seems pretty decent given the stated runtime is 2h 40min with a fenix 3500mah battery.
Well it easily met the stated runtime so I’m going to stop and recharge it now to avoid it getting too low.
Seems to be well on track to hold close to its rated capacity.
I might try again and see if I can do a full cycle, what’s the lowest voltage I can safely discharge to?