Battery
A rechargeable battery is recharged by reversing the chemical reaction that occurs within the battery.  But a rechargeable battery can only be recharged a given number of times (recharge life).  Even built-in batteries, cannot be recharged forever.  Moreover, each time a battery is recharged, its ability to hold a charge goes down a bit.  Non-rechargeable batteries should not be charged as various harmful substances can leak out, such as potassium hydroxide.