I can certainly appreciate your approach and perspective as an engineer! I browsed around to learn more about this particular light…several good reviews but none had everything we hope to learn. Seems they ship the light with the protected cell - that is more de rigeur lately than for any particular benefit, truthfully - but the light has very good and apparently dependable low voltage cutoff protection, and seems to have a good charging circuit as well (often the charging circuits in our lights aren’t the best by any means, but serviceable). You may be aware that pretty much all cells have some built in protections (mechanical) but the added protection boards serve to cut current in the event of over voltage (defective charging) or over drain (failure of LVP or short circuit)…but they also have limits on the current they can allow to flow as well as adding resistance, which work against max lumens, mostly. There’s nothing wrong with using protected cells but when we have dependable drivers there’s nothing wrong with using plain bare cells. Major brands like Acebeam and others have moved toward protected cells just as CYA, since there are so many people still uneducated about safe lithium use, and a few lawsuits (Olight, mostly) cause them to pause and take the $$$ safer route.
The inner signal tube on this light seems to have prevented everyone from measuring current draw, but guesstimating the binning on SFT-40 emitters and the 4200-ish turbo lumens that Zeroair measured, it’s probably pulling about 12amps, maybe a touch more, but only for a minute. That’s fine even on most 10a CDR cells (although a bit harsh, heatwise, in terms of longevity/cycle life). So given that, and understanding that Acebeam is fudging a little calling the cell 5100mAh, we can kind of guess what type of cell they’re using. Looks like they’ve done LG cells a lot in the past, so it’s probable that they did something like the LG M50 flavors, and those are comparable to Samsung 50E (50G would be better) and several others…and if you chose a “lower” capacity cell in the 4000-4500 range it may not really be any difference in actual run time unless you primarily use the light in lower modes…lots of turbo and high mode and it may be a washout where the lower drain 5000 cell will fall on its face and give the same run time-ish of the lower capacity high drain cells. This light just isn’t pulling a ton of amps so really you can pretty much use what you want. I might not recommend the Samsung 50S just based on its sensitivity to heat and greatly reduced cycle life as is being shown in tests (losses appear to be more severe and much earlier than our usual cells), but it’s a high capacity cell with great voltage retention (just at a cost, and this isn’t really its intended application…probably best with lower currents and float charging). The important thing to remember here is this light has a current-regulated driver, so it’s not like a FET driver that turns open the spigot and can make a battery that unhappy…most 21700 cells aren’t going to complain and you don’t need the high drain to accommodate what this light will draw since it’s so brief.
Illumn is one of our long term great suppliers and they have the similar usb-port Acebeam cell in stock, singles…have to pay shipping and as of recently they had to rescind our small BLF discount, but it’s still a good deal. https://illumn.com/21700-acebeam-imr21700np-510a-5100mah-20a-high-discharge-protected-button-top-usb-c-recharge-port.html
Andrew & Amanda have been around a long time…dependable. They have the same cell you got…same price, plus shipping…they may float you a BLF discount if you ask. They had a new rep that was posting on the forum a lot last year but she seems to have disappeared. I think they’re in California but I can’t recall for sure. Acebeam 25A Rechargeable 21700 Battery - 5100mAh
If you really want a protected cell, personally I would straight away buy this one from Liion before I would purchase the Acebeam cell (sorry if this was linked above…just skimmed). I don’t know if they’re using a Lishen or Sinowatt cell in here or what, but they’d probably tell you if you ask them. Liion is a great supplier, different than the rest. https://liionwholesale.com/collections/batteries/products/protected-5000mah-15a-21700-button-top-battery-wholesale-discount?variant=39848920744005
Might be able to find the same stock cell at Killzone, Longhorn Tactical, Battery Junction, Brightguy, etc…didn’t check those sites out.
Here’s Zero’s review…his graphs/measurements are helpful sometimes, but here he has a couple showing the LVP as well as repeats of the charging…both good and reassuring (not always the case for many lights): Acebeam Defender P18 Tactical Flashlight Review - ZeroAir Reviews
Nick’s review at 1Lumen, overlaps with above but he took the time to try out different cell lengths/types (for fitment only): Acebeam P18 review | Tactical / general purpose flashlight with 5,000 lumens | 1lumen.com
Similar comments from our German friends (no English option…need to translate): Acebeam Defender P18 Review | Taschenlampen Forum
In that review they linked a youtube teardown video of a similar earlier Acebeam 21700 cell…using the (now defunct maybe?) LG cell. If you haven’t seen before how protection circuits or buttons are added to stock cells, this is good to watch (although I would use a little different technique than he did). We have a wonderful electronics wizard who has done zillions of battery and device tests for us over the years…he’s on hiatus but he did test this same cell, and it’s clear that Acebeam is fudging stats, which is typical with rewraps and the big brands. Doesn’t make it a bad cell, just goes to show that they may not be selling what they’re advertising, and you can do the same or better by yourself and choosing a standard cell or at least a differnt vendor for similar.
HJK’s BLF post here: Test/review of LG 21700 M50 5000mAh (Grey)
And here’s his review on his website…if you nose around it’s a wonderful site, so much information. I’ll link his battery comparator for 21700, too (pick a cell from the drop down, then pick a second, and on the graph you can check or uncheck various currents and see how they do vs. another…great tool).
https://lygte-info.dk/review/batteries2012/LG%2021700%20M50%205000mAh%20(Grey)%20UK.html
Comparator (21700 lumped in with 18650…other size groups linked at the top of the page): Battery test-review 18650 comparator
He’s got some good general articles, too…scroll down the page and there are several on cell disassembly/inspection showing add-on circuits and such. Actually a really neat one on disassembling 9v batteries, too. Information