*I apologize if this gets duplicated, but I received a 'server-error' when I posted this a moment ago. Moderator, feel free to delete this disclaimer and any copies. ___________________ Wait - someone out there is still paying for single-use Alkaline batteries instead of using rechargeable ones?

OK...seriously now: Several things at work here.

Cap Material The steel used for the bottom cap will not be heated to a temperature that would allow annealing or any change in the modulus of elasticity, so that is NOT a factor.

Shape The shape of the bottom cap IS a factor if attempting to compare battery bounces between different brands. So don't. Comparing any number of bouncing batteries to others of the same brand should indicate a difference that does appear to reflect the state of the batteries, particularly between 'new' and 'nearly discharged'.

The discharge of a battery MAY cause the shape of the bottom cap to change, if there is pressure against that surface as a result of discharge. This could be a factor here, through any crystallizing chemical structure (physical expansion pressure) or production/release of hydrogen or other gases in the sealed cell. Gas pressure may also cause a slight plastic deformation through hoop stress of the barrel diameter, rather than at the base. If such gas pressure is sufficient, and is contained, then it is possible that this may contribute to slightly greater 'bounciness' in general; In this case, the 'newer' battery is a somewhat softer fill of zinc surrounded by manganese oxide, with no off-gassing as yet, and does include a 'pressure expansion seal' that can push outward against the bottom cap (negative terminal).

Inertial Reaction to Impact Ever hit a hard surface with various hammers of different types of metal? Ever used a 'dead hammer' full of shot? Any 'softer' material, or especially an object full of looser fill, will absorb more of the impact energy internally. The 'bounce' will be measurably less than two fully crystallized, high modulus and hardness, denser materials making contact. Same reason, inversely, that a 'fresh' baseball will react livelier and travel further out of the park than an old practice ball that has been loosened up inside through repeated crushing blows. The positive electrode mix is a paste of manganese dioxide (with additives). The negative electrode is zinc powder in a gel with KOH electrolyte, which is never used up, which is why old batteries will still leak. Only a 'leaking' cell will form that annoyingly corrosive potash fuzz when the KOH gel gets exposed to carbon in the air. But the zinc powder will become crystalline wurtzite ZnO, still relatively soft but stable, and the MnO2 will become crystalline Mn2O3.

So - neither electrode material is 'rigid' when fresh, but the oxides that are formed as the cell discharges do create the somewhat harder, more crystallized contents left behind.

Predictably then, a discharged cell, with a bit of gas pressure and harder crystallized contents, should in fact 'bounce' (a tiny bit) MORE, than a fresh alkaline cell of the same type and construction.