I ran an MCE warm on high and it quit at 20 minutes, but it would come back on if I hit the switch off then back on. The batteries, which were AW RCR123's read 3.7 after the shut off. The light was quite warm when it shut off so I'm wondering if this is a safety feature so it doesn't overheat. I didn't continue to run it to see how much more time I would get, but I'm sure based on the battery voltage that more time was left. Gene's web sight advertises 45 minutes on 2 cr123 primaries.
I also measured 1.4A on high, while Gene's web site says 1300ma's @ 6V. Does this mean my LEDs have a lower Vf and I can expect hotter temps and lower runtimes? Or, is it because I'm running rcr's with a starting voltage of 4.2V? It is also possible that my DMM, which is a cheap Walmart item, is not completely accurate.
The "protected" batteries cut out when the voltage dips below a certain threshold. When off most rechargeable batteries recover somewhat. So turning off and back on is no surprise. Its normal. Doesn't mean you shouldn't just stop and recharge the batteries. Has nothing to do with Vf of the actual LED, its in a regulated driver circuit.
Don't worry about the exact current levels. Especially with a cheap meter. Non rechargeable batteries hold more energy than rechargeables do and the amount varies. The advantage of the rechargeable is that you can recharge it. You aren't going to hurt the MC-E by running it up to 20 minutes at a time.
The 2 stage ring replaces the regular module holding ring in the back of the head. You simply screw it in behind the module till the module is very snug, don't torque it down like your life depended on it.
You can then turn the entire head of the MD2 a quarter turn and you will have low mode. Tighten it up fully and you have full power.
Topping off means to recharge the battery without waiting for it to be fully drained or down to the cut off level. To just charge it when you are done using it. Most batteries will last much longer if you don't wait till they are dead or near dead to recharge them. Lots of little recharges instead of a few full power recharges.
Gene will be selling the heads separately at a later date. He is too swamped with orders right now to make the heads available separately. In the long term everything will be available individually and you can pick and choose your own modular system. More top secret accessories are on the way.
Run times vary with batteries. I would say 20 minutes with rechargeables to drive an MC-E is about right. roughly 45 minutes with primaries also sounds good but don't expect it to be exact. They will start to fade but won't cut off so you will get more lower level run time and warning to change batteries before it dies.