> I've definitely bought bad (really cheap..) store-brand batteries that lasted inconveniently short. If it's Duracell I know it's good.

If you bought the cheapest battery on the shelf, then it probably wasn't an alkaline battery. A heavy-duty battery (carbon-zinc) has half the capacity of an alkaline.

If you buy Duracell, you know you will get at least an alkaline battery. Duracell simply does not sell heavy-duty batteries, hence the brand name: the durable cell. It's mostly a matter of brand positioning, rather than technology.

Rayovac uses one brand for both alkaline and heavy-duty batteries, which cheapens their brand when a consumer buys the wrong type and all the batteries die a quick death. Energizer addresses this problem by selling heavy-duty batteries under the Everready brand.