Solarforce claims 3.5 hour run times on high with their low voltage XP-G drop-in and an 18650. That seemed a bit ambitious, so I decided to test it. Here's how things went:
Test 1: At 1.5 hours, the light was going strong. I got distracted and came back to check at 2 hours, but found that the light had turned itself off. I tested the battery at 3.14 volts. I didn't think much of it, so I recharged the battery and decided to do a second test with a different battery.
Test 2: At 1.5 hours, the light was going strong. I kept a closer watch on it this time and a few minutes past 1.5 hours, I checked and noticed that the light had turned off. I tested the battery at 3.03 volts. I decided to turn the light back on a see how long it would last, but it turned itself off again almost immediately and the battery's protection cicruit tripped. I know this because the battery measured 0 volts. I also know that I didn't kill the battery because my pila is happy to charge it without drama.
On one hand, current draw on high is initially 1.5 - 1.6 amps, so one might expect a 2200 mAH battery to last about 1.5 hours. OTOH, the battery was above 3 volts in both cases, so I don't see why the light would turn off. In both tests I used AW 2200 batteries, but different batteries, so a single overzealous protection circuit wouldn't explain this. I'll also mention that I've pushed down to just above 2.7 volts before without tripping the protection circuit.
Resting voltage isn't the same as voltage under load (not that you should bother with these levels, 3.5V at resting is basically empty). Also 3.5 hours would be with AAs or CR123s where the current draw is lower than with an 18650.
Yes, I agree. Mine pulls 1.75A on high, I get close to 1.5 hours runtime on high with HI-Max 2600's, would not expect it to last longer at that amperage.
I guess one of the things that surprised me here was that the behavior was very different from that of my solarforce 3-6V XM-L. That drop-in seems to go into some sort of "moon mode" when the battery is weak, so it doesn't have the abrupt cut off that the XP-G drop-in has on high.
I too don't understand how to relate Solarforce's 3.5 hours runtime on a 18650 Lithium. They do make that exact claim. As a NOOB, it was definately a great factor in choosing their light and drop-in. I bought the XP-G, Cree (0.8v-4.2v)-R2L-3M, in addition to the 3.5 hr. runtime on as 18650, they claim 10 hours on medium, (they claim 40% of max.).
My tests got 57 minutes on high, and with a fresh battery, about 4 hours on medium. The light was uncomfortably hot to the touch on high, but just slightly warm on medium.