This may be sacrilegious, but it seems to me that the only time any of this battery/current question makes any difference is on turbo, or possibly with some very cheap batteries on high. When you are on any setting other than maximum, the driver is limiting the current flow to what that particular level wants. If the battery is good enough that you can tell the difference in light level between the highest and next highest level, then the battery can supply more than enough current for anything except the maximum level (BUT NOT NECESSARILY SAFELY). With most drivers the maximum level is defined by the driver placing the battery directly across the led(s). In this case the light level/current will be defined by the internal resistance of the battery, and Vinh has determined that the VTC5A is the battery that can deliver the lowest internal resistance. If the battery is poor enough, the next level down may indeed be limited by its internal resistance, but I've found this to happen very rarely--I haven't even THOUGHT of trying it in any of Vinh's monster lights. For normal lights in typical use I have no qualms using cheap high capacity but poor internal resistance batteries, as I don't intend to use the light at levels that would make any difference. If I do, it will be for a very short time, and the light level won't be what it could be, but I don't really care. I do that infrequently, because a cheap battery can overheat very quickly if asked for enough more than it can deliver.
Before you tell me that that's a dangerous thing to do--yes, it could be, and certainly if you were to literally short the battery it would react more quickly than you would know, as it would happen before the body of the light indicated a problem, but if you know this in advance, the led resistance is certainly more than a short, and you will not be in danger for a few seconds of high level light. I recognize that this would be a very bad statement to make to the general public, and Vinh certainly tries to protect himself as best he can by sending a serious disclaimer with every light, but I feel that this particular audience is more than aware of all this and that I'm therefore not doing any damage. Don't get me wrong, I'm not advocating running powerful lights on high with cheap batteries, I'm just pointing out that you can use those batteries for normal lighting if you're VERY careful about high levels, remembering that a battery can explode before the light body gets warm if it's put under a large enough load.
