Okay. Finally getting back to report on how my purchase of FastTech’s “Authentic Sanyo UR14500P 14500 840mAh Li-ion Battery (2-Pack)”.
These unprotected, flat-top cells, while fitting safely in the tube, did not at the start work in my Zebralight H502, due to the flat top (lack of button top). I purchased a package of 3mm diameter magnets on Ebay. This worked perfectly. Many thanks to JohnnyMac for the tip here:
To repost what he wrote:
I did not use any glue. I think some people here might say there’s a safety issue is the magnet somehow touched the flashlight tube, but I don’t see how that could happen. But, for safety, please consider this and act at your own risk. My battery is attracted to the metal contacts at the center of the Zebralight, as well as the metal top of the Sanyo flat top (which does not go all the way to the side, and there’s a wrapper, too). I just place the little magnet on center of the positive side, slide it straight down the tube (I hold the tube straight upside-down to ensure it goes down straight, and let gravity do the work), screw on the cap and it works!
NOTE: I first tried a wider magnet I already owned (5mm? 6mm?), and it was TOO WIDE. It did not work. I think 3mm is the ideal size, like JohnnyMac said.
The best part about using the Sanyo UR14500P is, the tailcap does not feel like it’s crushing the battery anymore, to make contact! Yeah! I have now found (for me) the ideal Li-Ion cell for the H502 (for price, size, quality, and capacity). Zebralight should NOT have made it this difficult!
I don’t know if it would be a “feature” or “defect”, but as a result, the battery now does not immediately slide out of the tube when the cap is unscrewed. The magnet holds the battery inside. With a light shake, the battery will disconnect and slide out. Luckily, the magnet stays on the battery, not inside the flashlight.
From the reviews posted at FastTech, the 14500P’s are now of new manufacture, and just about matching the rated capacity of 840mAH. The current price has gone up from my last post from $9.94 to $10.01 for 2 cells.
https://www.fasttech.com/products/1287511
FastTech also has a welded-tab version of the battery, model 14500L2, $5.64 for 2 cells:
https://www.fasttech.com/products/1420/10002603/1193200
But the reviews are not as good, claiming a capacity of about 500mAH—however half the price of the 14500P, and probably still better than the Trustfires I got from DX for about the same money. Rememer, the point here is to find a quality, safe, UNPROTECTED Li-Ion cell for the Zebralight, so it will fit properly. One reviewer stated that he was able to remove the bottom tab, and cut off part of the top tab, and folded it over to act as a “button”. I’m not sure that would work in the H502 (although probably easier to place a solder blob onto), and personally I get nervous using metal pliers (or solder) on lithium cells. But for savvy BLF’ers, this might be a budget choice or experiment (and no need for a magnet).
PERFORMANCE: from my previous test, above a certain voltage, the H502 regulates High-High current to 1.0 amps, and High-Low current to 0.5 amps. So, I expect that the brightness is the same, over my Trustfire flames, just the runtime is much improved. On the highest high (which I only use briefly, and infrequently), it gives about the same light output as a cheap, large Ebay XM-L zoomie with the front lens removed running about 1 to 1.5 amps. (Which makes sense). And which is really all I wanted from the beginning. NO ill effects noted to this point (again, I’m careful). And obviously, far greater runtime than my low-quality Trustfire flames.
IMPORTANT OBSERVATION ABOUT TRUSTFIRE FLAME 14500’s: while this has already been noted by others, it’s important and I can personally verify this: TrustFire uses different cell manufacturers for the same “Flame” cells, and hence slightly different lengths of cells. This explains the variety of experience and reviews for these. I have 1 cell which will not fit in my H502 at all, and 1 which does fit, but barely. So if you already have Trustfire flames, and an H502, don’t force the tailcap over your protected Trustfire, just because one (barely) fit in mine. Just get a quality unprotected button-top 14500, or make a button yourself.
SAFETY NOTE: Because the H502 can be easily accidentally activated due to the nature of the soft switch, unscrew the tailcap a little before you carry this in a pocket or pack, to “lock out” the power. I also recommend keeping the High mode normally on the “lower” High selection (0.5 amps), just in case you forget.
REGULATION NOTE: Regulation does not necessarily mean “constant brightness”. Brightness curve best translates to watts being used. Watts = Amps x Volts. The H502 regulates amperage (amps). However, the voltage of your cell drops as it gets used. So even though the amps stay the same, with less voltage, there is less power being drawn, and hence lower brightness as time goes on. I think most people see regulation as a way to maintain brightness till the battery just can’t give anymore. However, with the H502 at least, the regulation effectively acts as a safety cap, or a limiter, so that the battery’s full power cannot be used. For instance, on High-High, the H502 regulates (or limits) the current to 1 amp exactly. (True “digital regulation”, unlike the fake Ebay/DX/Kaidomain claims.) At 4V (freshly charged li-ion), 4v x 1A = 4 watts. As the cell gets used, let’s say it drops to 3.0v. The H502 is still regulating it to 1 amp. But 3v x 1A = 3 watts. Substantially less bright. The light is nevertheless regulated. With the H502’s regulation, the only way you can increase brightness (wattage sent to the LED), is by increasing your battery voltage. And Li-Ion 14500 cells are basically as high as you will go. If this is new to you, I know, it’s disappointing. This is why crude, cheap lamps can sometimes be more exciting.
CONCLUSION: The Sanyo 14500P unprotected cell is an excellent cell, perhaps the best Li-Ion cell, for the H502 if you can make a button for it and can be wise with your usage of High-High mode. The H502 remains my most-used flashlight. Let’s face it. Unless you use mostly low modes, the runtime from any 14500 isn’t going to be terrific. The H502 needs all the help it can get.
RANT: I maintain that my measurements (post 3) prove that the H502 was designed for use with Li-Ion cells. Or at least cells exceeding 2V. The more I learn about this light’s innerworkings, the more I become confused and miffed as to why Zebralight chose to 1) design this light without room for protected cells, and 2) declare that Li-Ion cells are “not supported”, to the point that experienced, senior flashaholic forum members on here and CPF declared some kind of orthodoxy (without actually testing) that Li-Ion cells “would not work” in the H502, and that the H502 was “not designed” for use with Li-Ion or higher-voltage cells, both of which I have proven false. Cell length cannot be too long (protected), and the cell must have a button top. Those are the only hard limitations. I may just confront (ask) ZL about this. I think it’s time.