charging rechargeable batteries

is it better to wait until batteries are depleted fully, and then recharging, OR is it fine to recharge batteries when it's half full or partly full?
i'm referring mostly to laptops, mp3 players, phones and the like. i guess i'm slightly concerned about improper charging.

>>9
No, the memory effect is not real, or at best very rare under normal circumstances. What people call the "memory effect" is actually voltage depression, where the battery's voltage drops off suddenly (which appears to anything with a battery meter as a sudden drop in the battery's charge level). It can be fixed to some extent by doing cycles of full discharge/full charge, which is why the better battery chargers have that feature. Strictly speaking the "memory effect" refers to a different problem that occurs only when a battery is discharged to the exact same level repeatedly (as happens on satellites that spend a consistent amount of time in the earth's shadow during their orbit).