My Xeno is brighter on 1.2V vs 3.6v, any ideas?

Just got my Xeno E03 today but my 14500 batteries that I ordered haven't showed up yet. So I tried it out with a Duracell rechargeable AA NiMH 1.2V rated at 1800mAh. It's decently bright. But I wanted to try the light at 3.6V so I drove over to Radio Shack and paid stupid money for the only 14500 they had... an Enercell Lithium (non-rechargeable) 3.6V rated at 2200mAh.

The light is actually brighter on high on the 1.2V cell than the 3.6V. Although on 3.6V the low is brighter, but the medium and high levels are dimmer.

Doesn't make sense.

I did read a few of the battery threads but did not see this specific issue discussed. Any thoughts? Thanks.

Is the Radioshack battery charged to 4.2 volts?

Edit: My Duraloops push over 2 amps this Enercell must be weak in the amperage department.

The light runs essentially on DD w/ lithiums, so I suppose it's possible that the enercell really sucks at delivering current and the higher voltage is actually a handicap. What's unusual is that this light isn't all that bright on AA's in the first place, so enercell must REALLY suck if this hypothesis is true.

It's possible that the enercell doesn't supply enough current? The duraloop (duracell branded sanyo eneloop) cells can handle a fairly high current, so even after losses from the boost circuitry, might be delivering more to the emitter than the lithiums. Hard to tell without a multimeter handy.

Just a guess. Good luck with real 14500's though!

Hmmmm... The Enercell tests at 3.65V, maybe it's just a low-quality cell that can't handle the Amp draw? Bummer for sure.

The plot thickens. My rechargeable Duracells are 1.2V. I put in an Alkaline Duracell at 1.5V and it was noticeably brighter. On high I compared it to my Fenix PD30 on Turbo (supposedly 215 lumens) shining at my garage wall about 10 feet away. While the hot spot of the PD30 was much brighter, the overall usable light of the Xeno E03 was way better. I can't wait for my 14500 cells to arrive!

Well, the alkaline'll be brighter for a few minutes.