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it's been touched on above, but like the vast majority of things in diving, this recommendation is out-dated and not founded in current state of the art and understanding. Continued fear mongering and ignorance keep rules like that in place.
So why did it come about in the first place and why is it no longer valid?
Alkaline has a predictable discharge curve meaning that the voltage is relatively linear to state of charge. This means that with a multimeter you can quickly check the batteries and know their state of charge and that is one of the main arguments for it. When was the last time you saw someone at a dive site with a multimeter?
Old chemistries that are no longer used were much less stable and more importantly they historically suffered from memory effect where their duration was no longer predictable. New alkalines that exhibit negligible self discharge and are consistent in capacity obviously are superior for that.
Once NiMh from Sanyo/Eneloop came out that helped to solve the self-discharge and memory issues. They still have a flat discharge curve, but with the smart chargers that can cycle the batteries, I cycle before a big trip and then I know definitively what the capacity of the batteries are and know that they are fully charged. The cycle function fully charges, discharges to the "safe" level, then fully charges again.
The single 18650's have two HUGE advantages to all of the other chemistries though and they are the energy density that allows them to stay small, but more importantly they can handle big discharge loads. A Cree XML-U2 that puts out 700ish lumen *all of the single 18650 lights with that emitter put out about that much, but they usually claim 1000-1200 lumen* is comparable to a 10w HID in terms of light output. That type of drain is not able to be handled by most alkaline cells without a significant amount of them, and certainly not for an hour long burn.
With backmount, the traditional light location never really pushed for backup lights to be smaller. With sidemount and essentially losing the "traditional" light location, there is a push to smaller lights, but it is also taking advantage of the new technology in terms of LED efficiency, battery chemistry, etc. The argument for "simple" lights because of "less failure" is gone since all LED's have control boards in them so there is no getting away from that anymore, some of the push buttons that are magnetic still have no thru-holes, etc.
This type of issue applies to CCR's where people argue that analog electronics are more robust than digital *pre DiveCAN vs. current*, anyone who still uses tables/ratio deco instead of computers, trimix pretty much everything, dive shop sales models, teaching curricula, many other aspects of our sport. The lack of understanding of how and why the technology works leads people to get defensive when questioned and they fail to research and learn how and why things work. It's easier to stay ignorant, and our industry is really good at it, and I applaud you for having the balls to ask the question because the vast majority do not.
So why did it come about in the first place and why is it no longer valid?
Alkaline has a predictable discharge curve meaning that the voltage is relatively linear to state of charge. This means that with a multimeter you can quickly check the batteries and know their state of charge and that is one of the main arguments for it. When was the last time you saw someone at a dive site with a multimeter?
Old chemistries that are no longer used were much less stable and more importantly they historically suffered from memory effect where their duration was no longer predictable. New alkalines that exhibit negligible self discharge and are consistent in capacity obviously are superior for that.
Once NiMh from Sanyo/Eneloop came out that helped to solve the self-discharge and memory issues. They still have a flat discharge curve, but with the smart chargers that can cycle the batteries, I cycle before a big trip and then I know definitively what the capacity of the batteries are and know that they are fully charged. The cycle function fully charges, discharges to the "safe" level, then fully charges again.
The single 18650's have two HUGE advantages to all of the other chemistries though and they are the energy density that allows them to stay small, but more importantly they can handle big discharge loads. A Cree XML-U2 that puts out 700ish lumen *all of the single 18650 lights with that emitter put out about that much, but they usually claim 1000-1200 lumen* is comparable to a 10w HID in terms of light output. That type of drain is not able to be handled by most alkaline cells without a significant amount of them, and certainly not for an hour long burn.
With backmount, the traditional light location never really pushed for backup lights to be smaller. With sidemount and essentially losing the "traditional" light location, there is a push to smaller lights, but it is also taking advantage of the new technology in terms of LED efficiency, battery chemistry, etc. The argument for "simple" lights because of "less failure" is gone since all LED's have control boards in them so there is no getting away from that anymore, some of the push buttons that are magnetic still have no thru-holes, etc.
This type of issue applies to CCR's where people argue that analog electronics are more robust than digital *pre DiveCAN vs. current*, anyone who still uses tables/ratio deco instead of computers, trimix pretty much everything, dive shop sales models, teaching curricula, many other aspects of our sport. The lack of understanding of how and why the technology works leads people to get defensive when questioned and they fail to research and learn how and why things work. It's easier to stay ignorant, and our industry is really good at it, and I applaud you for having the balls to ask the question because the vast majority do not.
