There are many types of non-rechargeable batteries, but old-fashioned AA or AAA alkaline batteries are called a "dry cell" because there's no liquid. This makes it less likely for things to go wrong. You have two materials on the inside that want to react, but are separated from each other. Then you connect them electrically (with a wire). Now, the reason a battery doesn't lose its charge is because the circuit is open when the battery isn't in use. When you put the battery in a device, you connect one metal terminal to the other, creating a closed circuit (a loop), and the reaction takes place, generating electricity at the same time.

Interestingly, because the batteries are made of solid, dry materials, it sometimes takes a while for it to react. You might have noticed that when your batteries die and you leave them for a couple days, they "magically" come back to life for a little bit. That's because the solid materials on the inside have had time to move around and adjust, and are able to react again. (This is why alkaline batteries aren't good for digital cameras or other devices that require a lot of power really quickly, and is why you should use Lithium or NiMH batteries for these applications.)

This is an interesting site where you can see a nice picture of how a battery works.Please click on it, you will enjoy it.

A battery consists of four components: two anions (atoms or compounds with negative charge), and two cations (atoms or compounds with positive charge). Moreover, these ions are of a type that can change into each-other with the acquisition or removal of charge. One of the anions is bonded to one of the cations in the plus end of the battery, and the other pair of one anion and one cation, are bonded to each-other in the negative end. However, the anions and cations are not ideally bonded to each-other: the anion in the positive end would bond more strongly to the cation in the negative end, and vice-versa. As a consequence, when a conductor is connected to each end of the battery, current flows in such a way as to change the anions into the anions they would bond more strongly being, and likewise for the cations. When all of the ions have changed to their most strongly-bonding conformations, the battery cannot transmit any more current and is "dead".