Re: SD series headlamp from Spark Tech, SD52 prototype updated
The positive contact makes contact with the center of the positive pole of the battery. The negative pole makes contact offset from the center of the negative pole. This works quite well as a reversed polarity protection as the negative spring cannot make contact with the smaller positive pole of the battery. The extra space around the battery isn't deep enough to allow a larger battery to fit. If you remove the battery then take a picture you'll see that the hole for the battery is only large enough to fit an 18650 and the hole is offset to one side, away from the emitter pocket.