I've never look at a AA and said, "Wow, someone really put a lot of thought into this packaging!" On the other hand, now that they're going out of style, I've really started to appreciate the idea of a solid, standardized battery format. So, we're going back to square one as far as portable power standards
go, why not start fresh?
What I'm thinking is a standard, or set of standards, for a threaded connector. The threaded portion would make up one terminal, let say negative. Two domes/arches, or a dome and a plate, would sit in the center and comprise the positive terminal. Dimensions of the threading, height and diameter of the socket, height and diameter of the positive terminal, and maximum external diameter of the battery would be proscribed; maybe 15mm.
The battery would be shaped like a large, squat motherboard standoff. The positive and negative contacts would pass straight through the housing, to the socket at the base, so that when one battery was screwed into another, they would be connected in parallel.
Say you need a flashlight. The light would just be a small can, with a few LEDs on one end. The other end would have a socket with a plug in it. You unscrew the plugs, screw in as many batteries as you expect to need,end into end, and screw the plug into the last battery.
Supposing the batteries were lithium-ion polymer, they could be constructed thus:
The LIon battery is made in a thin mylar wrapped ribbon, with a terminal at each end. The ribbon is rolled into a coil with the positive terminal in the center. Maybe there is a rolled sheet metal post in the middle, clamping around the positive tab. Maybe not. The negative tab contacts a thin walled tube in which everything is house. The ends of teh tube have thread pressed into them, and then a plastic of rubber housing is molded over the ouside of the bottom portion. Add a gasket at the shoulder and it should be reasonably water resistant when assembled. I think a li poly cell would put out the right voltage for an LED, though that's not really important.
*** I forgot to put this in before... the length of the batter is not specified. So, you might have a 15x4mm battery for watches and keychain lights, and 15x50 or so for flashlights, PDAs, whatever. This way manufacuter's can still make custom sized, cosmetically matched batteries and charge you something awful for them.
There might also be a larger, 40mm diameter/12v specification with the ribbons connceted in serial, internally. The larger batteries could also use a PCB for the center post, to safeguard the battery from excessive charge/discharge.
Longer batteries could have flexible center sections.