> Your feedback would be most appreciated! I’m a neophyte in this.
Im also new, I think the following is true
LiIon includes
IMR
INR
ICR
ICR is the old standard and are protected, because they have the least safe chemistry. They are not High Discharge, generally max out at CCA of 3A, and are usually button top
IMR and INR are High discharge capable, with CCA of 10A +–5
if I understand correctly lights with FET will take all they can get and be brighter, example the Anduril lights… by contrast, regulated lights such as HDS, will not exceed a preset brightness…
IMR and INR are often unprotected and flat top
> I think that flashlights themselves have a max continuous current that they can use, so I suppose exceeding that with a battery won’t improve brightness further, right.
yes w a FET, no with a regulated output light
> I wonder if all the batteries I’m finding are of sufficient quality. I’ve read that there are lots of “bad” batteries out there.
I think youre fine…
I dont think the scare stories apply… imo those are regarding cheap, no name cells that were pulled from old laptops and repackaged for deep discount sales on places like ebay. They were not brand new brand name cells.
now my opinions about brightness, derived in part from HDS FAQ
basically, 50% more lumens is not a large visual step, so trying to eek out another 20-30% more lumens, by hunting for the highest drain battery, will not yield a significant visual increase in max brightness.
better to adapt the eyes to use “enough” light, without using more than necessary, as this shuts down the iris and makes it more difficult to see with less light
it takes 30 minutes for eyes to downregulate to dark adapted levels… a blast of bright light is not helpful. Similar to taking a photo that is too bright, overexposed.
personal opinion:
chasing max lumens, is the road to perdition… it favors low CRI and Cool White… iow, high quantity, low Quality…
I always go for High CRI… I dont need thousands of lumens for a few seconds, I usually try not to exceen half the brightness potential of my lights… it doubles the runtime 
so your decisions hinge on
choosing a brand you can find, like the price of, and works in your light
I for example, have settled on the
Keepower 18350 Unprotected 1200mAh, which I buy from Illum
as the best for my Jetbeam RRT-01… I dont use max, though this cell IS high drain… what appeals to me about it, is the High Capacity (longer runtime)
even though that keeppower is a flat top, it happens to have a shape that works in my RRT-01, despite it having a reverse polarity protection ring, that makes other flat tops unable to reach the positive post on the driver. Actually using a battery in an actual light is sometimes necessary… The 750mAh Keepower for example, does not work in my RRT-01, because its flat top is wider.
protected cells are longer, some lights have built in LVP, so they dont need protected cells. Again Anduril for example, wants unprotected high drain for max output.
In an HDS Unprotected is also fine, as the light has built in LVP. However, because HDS is an example of a regulated output driver, there is no increase in output when using High Drain Cells.
IMR and INR, are safer than ICR, and IMR and INR are usually unprotected. This means no sudden darkness, instead the light just gets dimmer as the battery dies. I prefer this, as it gives me time to move to a safe place, instead of suddenly being stuck standing in the dark.
===
suggestion
you may want to sort your lights by driver type
example, regulated, wont get brighter with high drain cells
• Spy 007
example, UNregulated, will get brighter with high drain cells
• Lumenite 23650
btw, I encourage you to get a lightmeter, its much easier to measure differences in output, that our eyes are not sensitive to
.)