Please just don’t read this thread if reading long content makes you prone to gripes or flames. Just move along.
After years of following and researching Zebralight products, I finally took the plunge. It wasn’t all pretty, and this post comprises pretty much my own “review” as well, which may clash with others’.
Prior to purchasing my Zebralight H502 (my first Zebralight, and most expensive flashlight I own), I knew that it was designed for 1-volt cells, and that higher-voltage cells were “unsupported”—and what that meant, was never clear. With all the destructive tests we’ve seen, surely someone had tried it, and reported on it. Did it even work? Did it go pop? Believe it or not, although my research yielded many references to “14500 batteries not supported”, I found not a single reference to an attempt. Not saying there wasn’t one, but if so, I didn’t find it. Well, I figured I might have to be the gineau pig. I went through with the purchase anyway, and here are my results.
I won’t give a full review of the H502 with pictorials, because there are so many, but I want to share some impressions I hadn’t heard, or which contradicted what others said, or which validated some things which were disputed. The main thing being that (blasphemy), I actually wasn’t happy with this light. Why? Because on the supported cells (I used the recommended Eneloop, plus ‘Duraloop’ NiMH), it was only barely brighter than an XR-E on a 14500. I know their XM-L is intentionally underdriven; I get that. But it should be brighter than an XR-E, in my mind, especially for the price! I mean, until then my main headlamp was a C78 where I’d removed the head/lens, and literally rubber-banded it to an el-cheapo headlamp headband I had lying around from an unwise but very inexpensive headlamp purchase. Actually, the “chopped” C78 is great, super-lightweight, and the headband actually very comfortable, but the problem was: no modes (so it went balls to the wall on your 14500 until the protection circuit suddenly left you in darkness), and, being full flood, I wanted a little more brightness. This is why I spent more than 4x the money on the Zebralight. I’m amazed there’s really nothing in-between, unless you count the Ultrafire “H” series knock-offs, which aren’t really cheap themselves, for what they are (mostly XR-E’s until recently).
Upon actual use, I realized that a NiMH cell, regardless the efficient whiz-bang voltage boost circuit, was not going to produce the current to pull away from a well-driven XR-E in much of a significant way. This was a huge disappointment. And I felt foolish for spending $70 on something which wasn’t much better than I was able to whip up on the cheap. I wasn’t really planning on doing “unsupported” batteries, but I realized I had no choice (other than to send the unit back for a refund, which I didn’t want to do yet). Plus, I will say I thought the tint was awful. After reading George personally say ZL is “very picky about tint”, I was downright angry about the violet and sick-green hue. My C78 XR-E had a far better tint—a bit exaggerated in reds, but at least it HAD red! The H502 was pathetic on browns. And outside, things are mostly brown, especially in winter.
Keep in mind I had no idea what was going to happen when using “illegal” cells, so I was very worried. Did “unsupported” mean it would break it? Or break me?
First, I tried PowerGenix 1.8V NiZn cells. Still within 1.x volts, I wasn’t very worried. Well, I thought ‘this is better’. I was pretty satisfied. Even the tint seemed better somehow. But if you have any PowerGenix cells, you know how low capacity and unreliable they are. I knew I couldn’t keep the flashlight with the sole intent of using them with cells which aren’t really available to the general public anymore, and which were never very reliable or high capacity in the first place.
So then, LiFePO4. These are cells which are usually in the low 3.x volt range. Now THIS was good. Actually, the first time I tried them, I thought I had broken it, as the light wouldn’t turn on. I later learned I just hadn’t screwed on the cap tightly enough. Again, now being brighter, the tint was somehow acceptable, though still greenish. I read about this when it first came out, with owners speculating it was the glow-in-the-dark “reflector” at cause, with others claiming that was impossible. I own a good number of XM-L’s, and I’ve never seen a tint like this. The greenish hue matches the GITD, and it’s most prominent around the edges, where the GITD would stand to have its greatest effect. So, I’ll say I now believe the GITD “reflector” to be involved, and wish they had just given us a normal, polished metallic reflector of the exact same dimensions. It would’ve helped light output too, IMO. Anyway, most users of LiFePO4 have experienced its low capacity. I now had the light output I wanted, but the runtime was still no better than my stripped C78 on a Trustfire ‘flame’ 14500. But the best news was the light didn’t break, and on top of everything, all the modes worked! I remember old ZL headlamps and/or Fenix flashlights where li-ion cells were not supported, and people would get a surreal “High” mode (old Fenix AAA Cree running on a 10440), but no other modes—and in some cases, wouldn’t even turn off. That didn’t happen here. It worked beautifully, as if it were designed for it.
With great reluctance, I came to the conclusion that only a 14500 LiCo cell was going to give me both the voltage and capacity I wanted. So, I tried it. All I had were protected Trustfire flames, and I was hesitant to remove a protection circuit at the time, for mostly obvious reasons. Well, they are pushing the edge of how much room the H502 gives you. There’s NO spring at the front. And the cell comes nearly flush with the end of the battery tube. The spring must be compressed far enough to let the ends of the tube contact a conductive ring on the tailcap. I think a properly-shaped metal O-ring could help, but I didn’t have one. Anyway, the H502 actually gives you a brief flash of light to let you know when this ring makes contact with the tube. That’s quite handy when worrying about crushing a potentially dangerous cell.
Well, with the “illegal” LiCo 14500, I now had everything I wanted. Not super bright for an XM-L, but ahead of the XR-E enough to justify keeping it, and with runtime to match, and ZL’s famous interface (I’m not a fan of soft switches, but if you have to have one, this is it). BUT the light can and does come on accidentally if I’m not careful. Luckily, locking out the tailcap is super-easy. The tint seemed whiter—less violet and less sick-green. Though still having some of these attritubes, it was okay now. To me, the most interesting thing was that I didn’t really notice an increase in brightness, going from LiFe (3.x Volts) to Lithium Cobalt (4.x Volts). The driver seems (I stress that word) to me to cap it, like a boost/buck circuit working as if it were designed for that range of voltage.
So, with nearly zero official word on this, one is left to speculate on “why” ZL would design an XM-L where common sense would dictate a higher-voltage cell be used, and then not allow it. And also what is meant by “not supported”? Rumors can abound in this environment, and I’m afraid I might add to that, but here goes.
- I’ve seen George, the owner or chief of ZL say during my CPF days that Zebralight’s problem with li-ion cells is not the voltage, but the quality of the cells (and the safety issues which come with that). I found it ironic then, that they went and made a model for 18650 size. They now also sell 14500 cells made by Sanyo, but those still are not advertised as compatible with the ZL H502.
- It’s not that the circuitry won’t perform right at higher voltages. It works fine. Everything except the ‘battery checker’ function, of course, which always reads 4 pulses! 
- The length of the battery tube is so cramped, I wonder if they didn’t realize it was a little too short for protected cells until after production started? I don’t know. You gotta squish that spring pretty hard on protected cells, but mine do make it. I mean barely.
- Maybe they think there will inevitably be idiots who run it on High until something bad happens. And they’d be right. But measures can be taken here, such as time limits on how long a “turbo” mode can be on. In fact, I believe that’s done on the H600 (18650 verion)?!
- 14500 is supported on some other ZL models, so that kind of throws my above speculations into the water. Makes you wonder if they just thought their circuitry was too low-quality to handle it? A 4Sevens customer service phone rep basically told me as much when I challenged them that using a LiFePO4 and even LiCo worked just fine on their Quark Mini CR2, despite their owner’s assertion that the idea was “crazy”. I still disagreed with him. I’ve now owned 3 of them, and have used Li-Ion on all of them with no problem. I’m just not stupid with it.
I feel an importance to write about this, because to me, the H502 without higher-voltage cells does not justify the cost. Sure, some people just love luxury and quality, but remember, these are flashlights, and what they do is produce light. And if they don’t produce enough, what’s the point? This is in contrast with so many YouTube videos I watched of people saying the light (running on NiMH!) was “more than enough”, even those with the significantly lower lumen non-Cree versions. Whatever, fine. To each their own. But in full flood, there is the perception of less brightness, which is one reason few manufacturers have the nerve to release full-flood designs. I love full flood, but I also like to have enough light to see comfortably beyond my shoes, say up to 10-12 feet out. It can on Li-Ion; it can’t on NiMH. In all senses except battery tube length, this flashlight seems to have been designed to be used with 14500’s. And needs them to perform to full potential. Everything works, including memory. Low modes can still be super-low. It’s just beautiful. The only thing that’s missing is full ramp-up mode customizability.
Which leaves me wondering what the deal was for them to intentionally hamper their product. Was it the fear of a lawsuit if a 14500 blows up on somebody’s head? I honestly think that’s it. If it happens, they can point to their website and manual and say, “See, we told him not to”. But for users who want to try it at their own risk, it works great, as long as there’s no mishap. IMO they really should’ve left the battery tube longer for protected cells, instead of making it short and just telling people not to use li-ion. Because now I want to get an unprotected cell for it, yet I don’t really like the idea of wearing an unprotected cell on my forehead.
I still remain a huge fan of full flood/mules. But I am NOT a fan of GITD “reflectors”. While slightly useful, a GITD O-ring (or GITD elsewhere) would’ve been a better application. And, really, not necessary. Not only can I not figure out how to get this thing apart, I don’t know how they got it together. The front bezel has no dimples to screw off with tweezers, though I’d love to get in there, and “Bubba” some metal/reflective duct tape over that “reflector”. It’s the perfect shape and angle to be a reflector, and looks like like it was originally intended to be, yet it’s NOT. In fact, the membrane is partially transparent—you can see a bit of innerworkings inside. And surprisingly, the thing inside is NOT filled with thermal potting material. What? This surprised me. I’d like to get in there and squish some in. But it’s not gonna happen.
And, finally, one of the biggest downsides is worrying about losing it. I’ve already had a $40 4Sevens Quark Mini CR2 fall off my keychain in a parking lot, never to be recovered (whoever picked it up probably didn’t know what they had). With a beater SK68 clone or C78, you just don’t have to worry. In fact, you might just give the light to someone who’s really impressed by it (I’ve done that). If I leave the light at home or in my bag because I’m afraid to mar or lose it, what good is it doing me right then? And, that wonderfully anti-reflective glass lens is also wonderfully non-replaceable!
With that said, the H502 has become my most-used flashlight. Only because of li-ion, though. That’s right. Without Li-Ion, I would’ve sent it back. Between LiCo’s great capacity, and ZL’s efficient modes, you can get some really long runtimes when higher brightness isn’t required (which is most of the time—but sometimes you do). In fact, I even started using it indoors as an interior light, when a “night light” was too little, but an AC lamp was too much, such as pre- or post-bedtime with a partner. The right angle design comes in handy, and can be used while still attached to the headband. Or, angle it straight up at the ceiling. Or any angle in-between.
Lastly, I’d like to add that the Ultrafire knock-off headband I got from Kaidomain was actually of higher quality than the Zebralight one. While the elastic is probably not as durable, it is softer and easier to stretch (more comfortable). And, more importantly, it’s a fact that the Ultrafire people improved on the design of the rubber piece when they knocked it off (which is rare!). The Zebralight rubber part is too curved; it’s curved for the skull of a premature infant. There are even people who have ‘re-threaded’ the elastic thru the rubber mount in the opposite way, running the elastic through the flashlight mounting holes, so the overly curved rubber wouldn’t cut into their foreheads. My Zebralight headband now lives on my Trustfire Z1 right-angle light (a bad H30/H31 knock-off, except for the removable reflector, which is cool).