Continuous vs. Intermittent Runtime

I've noticed that most manufacturers and reviewers specify a "runtime" for each flashlight. And, based on what I've read, I'd guess that runtime means the same thing as battery life. For example, battery life for the popular Surefire L4 flashlight is advertised as "1-hour regulated, diminishing thereafter".

Assuming use of a regulated LED flashlight powered by two CR123 cells (similar to a Surefire L4), my questions are as follows:

1. Does the runtime spec always assume continuous duty?
2. Does intermittent use imply increased battery life?

Because I rarely use my flashlights more than a few minutes at a time, I'm curious to know if the CR123 batteries will provide more total minutes of runtime with intermittent use.

Answer to #1....yes
Answer to #2....probably

Interestingly, the Duracell spec sheet for CR123A tends to treat the battery as if it's used primarily for cameras and flashes. Last I looked it listed the battery life as something like "if used X number of times per day for X minutes at X number of seconds per picture".

Daniel

Most flashlight batteries "recover" after heavy use if let sit. It doesn't recover capacity but voltage. If you have something that requires a certain voltage to operate then the battery will be able to run it again after the recovery period until the voltage sags lower than needed for minimum operating range.

I call it springiness because some batteries tend to sag like a spring under a load more than others, heavy duty tends to be worse followed by alkaline and then rechargeables, I am not sure with lithium resides in this but my guess is around nimh or perhaps even less springy.

If you want to count total run time as useful run time or having to wait for a battery to recover then you may or may not get more useful capacity out of a cell depending on if you wish to mess with batteries being flakey at end of life, I find batteries near the bottom of capacity (nearly dead) get very springy the voltage sags more and recovers slower till it cannot even supply starting current after a long recovery period in the device used.

Yes I think an intermittent use test is much more
valuable than continuous run. Many of my lights
I have tested by running for 30 mins. and then
resting for 30 mins. They seem to get about
twice the runtime that a continuous test produces.
If the light has a really long runtime, I will
typically test it for 4 hours during an evening
and them finish the test the next day and the
next if need be. This gives me a much better
idea of what I can expect from the light. I use
alkalines in nearly all my lights.

-Rebus

Continuous run is probably easier to test (stick it there with a light meter) and it is also more conservative in a way, it portrays the worst case burntime you're going to get should you need to leave it on constantly. If your usage pattern differs from that, it's a nice bonus, you'll get more out of the light than advertised.

That to me sure sounds better than the alternative of manufacturers always over-inflating specs.. /ubbthreads/images/graemlins/smile.gif

I noticed this "resting" thing while messing around with my
trinty of 123 light's. (E1e, E2d, ARC LSH-P)I wanted to see how bright the arc would be on batt's the E's couldn't run anymore. so I switched back and forth between new and old 123's measured them, and a brand new duracell ultra after only after a minute or two, would test below 3V. let it sit for a while back up to 3.2V (or similar) same thing with AA lith's. interesting, any idea why this is? VDG

[ QUOTE ]
Lynx_Arc said:

I call it springiness because some batteries tend to sag like a spring under a load more than others, heavy duty tends to be worse followed by alkaline and then rechargeables, I am not sure with lithium resides in this but my guess is around nimh or perhaps even less springy.

[/ QUOTE ]

Yes, I've also experienced this "springiness" with conventional carbon-zinc and alkaline batteries. I've just started buying flashlights that use CR123A lithium batteries (thanks, CPF members!) and I don't know if the 123 batteries behave similarly to other battery technologies.

I've run a few of my CR123A lights (L4, Q-III, and T3) intermittently (i.e., a few minutes each day) during the past several weeks. When I remove the batteries and test them with a digital multimeter, I always measure 2.99 or 3.00 volts. I'm guessing these original batteries have provided approximately 45 minutes of full-brightness light thus far, and they're still going strong.

I figure all batteries have a little spring to them. I would bet that it is related to both internal resistance and maximum current output at rated voltage. I think batteries with higher current output have related inversely smaller springiness and due to that recovery time is either minimal or unnoticeably short.

Most likely larger current output devices have a larger pool of electrons easily available to use per unit area and instead of perhaps depleting the area of the cells near the anode or is it cathode? (the - end of the cell), anyway the electrons have to stabilize across the cell from - to + end and cells with fewer electrons in them have a higher percentage of electrons that must be moved around to reestablish equilibrium after a cell is put under a heavy load for an extended period of time. It could be alkalines have more electrons in them than nimh but without consulting a chemistry book I would have to say nimh have more *freely* available electrons in them, that is more *willing* electrons than alkalines. I assume the lithium cells electrons are less resistant to sticking around home (in the cell) than other battery chemistries also.