Just doing some reading and wondering if any manufacturers sell matched batteries. In my RC racing days you could buy matched cells and packs that were tested at the factory for capacity and charge/discharge characteristics; much like LED bins where the group similar cells together.
They came with printed labels that listed all the specs on the outside of the battery. Anything like this for typical flashlight batteries? Seems like this would lend itself to more reliability and performance.
I in a way do my own battery matching. I do a test cycle on a set of batteries to see how many mAh's they each hold. Any less than 80% are tossed into my recycle box. I group the rest in 5% ranges. I check each batteries voltage one day after they're charged using a 600 ohm load (because it has the lowest ohmage resistor on my battery tester before the higher current tests start) and look for any oddballs. I let the set sit for a month or two, checking the voltage once a week. This will test for a high self discharge battery. I keep all the above information in an Excel spreadsheet. Basically what I do is a process of elimination. Get rid of the low performers and group the rest so that they're pretty close to being the same. It is my understanding based on what I saw on a group of open box NMH's at a local electronics store that the mAh tolerance is ±10% for that manufacturer. 10% or 5% tolerance is probably as close as you're gonna get in a batch of batteries from manufacturers.
Nearly every hobby store, at least around here, sells matched cell battery packs. I have several ranging from 3300-4200 mah from my RC days. 6 matched loose cells, with excellent numbers can run you over $80 per 6. tower hobbies and R/C planet are 2 online stores that I am sure would have what you need.
I was looking at NIMH sub C cells on Battery Junction the other day and they had some brand that said they were matched. You could check those out and see if it is the kind of thing you are looking for.