my pedal sounds better with a dying battery???

[Mark Hammer]

In my experience different brands of batteries (all alkali) behave very different when aging. i.e. the expensive ones normally used to power rabbits stay above 9V for a long time and then rapidly loose current, while others tend to loose voltage quite fast but deliver enough current for a long time (lower series resistance?).
So my question is how can I measure the series resistance of a battery?

Most "expert" (i.e., high-profile player opinion) views of dying battery benefits will involve a carbon-zinc battery.  Carbon-zincs have a different junction between cells than do alkalines.  They are generally flat slugs with broader surface area.

Just to try and make more sense of the above, when you take apart alkaline batteries, you will find them to be 6 individual sub-AAA cells, lined up inside the metal shell.  The individual cells are metal, and are spot welded with little metal strips connecting them end to end.  In contrast, carbon-zinc batteries, like the red Eveready type siome are so fond of, are 6 flat slugs with much broader surface area between them.  They are NOT physically welded or bonded together, but merely sit in physical connection, the way a half-dozen batteries in a holder would sit.  Because of the internal chemistry, the two types change in a different manenr over time.  However, on top of this, because of the surface-area thing, the manner in which they can deliver instantaneous current is different.

Although I am not so fixated on this as to resist evidence to the contrary, my gut sense is that the broad surface area of C-Z slugs during their "dying out" phase allows them to momentarily deliver needed current in response to  transient peaks, but falter immediately thereafter.  When I was a teen, I had mononucleosis, and was a shut-in for lengthy periods and lived and died by myfaithful Mitsubishi transistor radio.  I could never get out to buy batteries, so it was always a matetr of conserving the batteries and using whatever power they had left wisely.  One of the phenomena I noticed was that as they aged they would respond initially to peaks but "retreat" quickly after.  If I set the volume VERY modestly, I could get the faltering batteries to deliver steady performance for a while before they faded out and needed a lengthy rest.  It is this "I can do a little bit for yu right now, but don't adk me to do too much" aspect of carbon-zincs that produces the sag, and it is the idiosyncratic current-delivery aspects of the flat C-Z slugs that is responsible.