Every battery has a finite lifespan, and this is given as the "recharge cycle" or "battery cycle." Put simply, this is the number of charge/discharge cycles that a battery can endure before being no longer fit for service. Many manufacturers offer this number. For example, Apple state that the iPhone battery is designed to retain up to 80 percent of its original capacity at 500 full charge and discharge cycles, while the MacBook Pro or MacBook Air is designed to deliver up to 1000 full charge and discharge cycles before it reaches 80 percent of its original capacity.
But most people think that they can dodge this charge and discharge by topping up their battery regularly so the battery doesn't get fully discharged. Unfortunately, you "cannae change the laws of physics." If you only let you battery discharge by 25 percent, then doing this four times counts as a cycle. Same if you do five charges after 20 percent discharge, or even 20 recharges after 5 percent discharge.
You cannae change the laws of physics!
However, what you can do is take advantage of this. How? By hooking your device up to a power source when you can. For example, playing music from your iPod or iPhone at home via a dock, or plugging your MacBook into a power outlet when convenient.
In other words, don't put the battery through unnecessary cycles. Understand that I'm not saying keep the device on charge all the time – that would also be bad for the battery because it needs a regular workout to keep its internal chemistry in good condition – just be aware of wasting cycles.