Eudamonium:
Yes...I calculated the required input power to achieve an output of 5W, based on the 6A figure provided by you...
Believe it or not but there is a whole world of brand name 18650 cells available out there (LG, Samsung etc...), which do come in in the capacity I mentioned and beyond. I own two DX cells, which as you mentioned are indeed complete crap...I power all my lasers from Samsung 2600mAh cells. I wouldn't trust a DX cell over .5C imo. Name brand on the other hand...lovely! BTW: A great source is a laptop which doesn't charge anymore...generally too expensive to fix...but can be powered through cord...battery pack is then useless and viola... very decent 18650 cells!
I don't disagree that a D-cell would be superior in terms of high current applications...what I am disagreeing with is the statement in the post I quoted.
Would a 18650 powering a 5W pump diode be ideal? Absolutely no, but it is more than possible.
Yes LiFe batteries are indeed quite nice, problem is capacity TBH, they are superior to LiIon in every other way. However I fail to see the relevance...