Strange behaviour of L1P with NiMH battery

I made a rough comparison test on my Fenix L1P with alkaline and rechargeable NiMH batteries. I ran periods of 15 minutes per night with each battery observing and comparing the brightness with bare eyes (no light measurements whatsoever). On the 7th night (that is, in the range of 1:30 to 1:45hs) the NiMH battery had a steep drop while the alkaline kept going strong. That doesn't match with the runtime plots that we have seen published here in CPF in various places. The batteries used are the SONY AA 2500 mAh (new and properly precharged) and a new DURACELL AA Ultra. Off course the test doesn't have any scientific or statistical meaning since there is no sampling and also no measurements were made, but is intended solely as an observation of the performance of both batteries in that particular light. The bottomline is: the Sony performed too poorly and the Duracell performed too good! Does anybody here observed something like that?

BobCol wrote: "I made a rough comparison test on my Fenix L1P with alkaline and rechargeable NiMH batteries. The bottomline is: the Sony performed too poorly and the Duracell performed too good! Does anybody here observed something like that?"

Just a guess/speculation -
could this be the self-discharge characteristics of NiMH batteries?

My experience - I have some older NiMH - 2sets of 4 Ray-o-Vac 1600mAh, and 1set of 4 jWin 1800mAh - that I used a lot in my older digicam. Since then I've changed digicams and these NiMH are left idle for much longer - and I've noticed that the 1800mAh jWins do self-discharge to the point where they won't even power up that digicam - whereas the 1600mAh Ray-o-Vacs don't seem to lose that much charge and give around the ballpark of the expected number of shots/capacity.

Conversely - I am cycling 2 of those 1800mAh jWins at a time in an electric toothbrush - and they seem to last for months - I recharge them "early" so that I do not over-discharge them - and the recharge time always seem short to me - however the idle unused pair seem to take longer on their "top-up" charge .... so go figure.......

BobCol said:

... I ran periods of 15 minutes per night with each battery observing and comparing the brightness with bare eyes (no light measurements whatsoever). On the 7th night (that is, in the range of 1:30 to 1:45hs) the NiMH battery had a steep drop while the alkaline kept going strong. That doesn't match with the runtime plots that we have seen published here in CPF in various places. ...?

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The runtime plots posted are for continuous usage versus your test's intermittant usage. Alkaline batteries "recover" somewhat after each usage, a characteristic which would explain the differing results of the two tests.

I'm not sure... sounds like possibly a combination of the two theories put forth by Unknown and parnass. If it's only one, I'd tend to lean towards parnass's thinking. Alkalines can seriously rejuvinate themselves given some 'off' time. If your test was done 5 minutes per night over a month vs 15 minutes per night over a week, I might lean towards it being a 50/50 thing but good NiMH cells shouldn't have appreciable self discharge over a week.

This just goes to show that for intermittant use, primary Lithiums are the way to go!

not all cells in a pack are equal either. i'm conditioning some energizer 2500's and three are topped off at around 2.53a with the fourth struggling to hit 2.30!

cratz2 said:

This just goes to show that for intermittant use, primary Lithiums are the way to go!

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i agree. i only use the L1P intermittantly and on a Li cell, it seems to last forever