I just received my L1D 2 weeks ago and it kicks ass.
I'm a little dissapointed with the on/off button though as sometimes it jams and doesn't turn on the flashlight or it goes straight to strobe and stays on that function. I'm gonna send it back to see if I can get a new one.
On the Fenix "D"igital series the modes are changed by simply tapping the the tail-switch to get a momentary Off.
However I used to have the habit of leaving my thumb on the switch after turning it on and still exterting some very slight pressure (habit from using forward/tactical clickies) - and the light sometimes would change modes "inadvertently" - once I realized what I was doing with the Fenix "D" series reverse clicky - I stopped doing that!
This may not be what's happening with your light
(which sounds just wrong) -
I agree that you probably should exchange it.
Back to the original question the Fenix L1D-Q5 is probably one of the brightest single AA flashlights out there - it also has 3 lower levels of light which makes it very versatile - there are lots of times when the brightest level is just not suitable for the task - eg: reading a map........
Fenix L1D-CE Comparison Review
it's not the Q5 - but probably a mere P3 Cree - however there is a lot of discussion about the light.
Fenix L2D-Q5 Comparison Review
it's the same head - just on a 2x AA body - the head is also the same as the P2D-Q5 (single CR123)
Consider this -
Fenix 4in1 Powerpack P2D/L1D Q5 Black Combo
this adds the versatility of using the head with a single CR123 (as the P2D-Q5)
Battery for the L1D-Q5 - rechargeable are recommended.
However about the previous suggestion of Energizer 2500mAh NiMH -
unfortunately it's one of the few NiMH's that has a pretty bad rep over at CPF (CandlePowerForums) for not being able to hold their charge for any length of time, with some reporting losing charge as quickly as a few days.
Suggest looking at the newer LSD (Low Self-Discharge) rechargeable NiMH batteries - the most well known is the eneloop (Circuit City did have them on closeout at $13/8), also Kodak Pre-Charged are well priced at $7.88/4 at any local WalMart.
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