Like car batteries, laptop batteries can be recharged up to 500 cycles. Once the cycle of 300-500 charges is done (in about 2-3 years), you will notice your a steady decline in your battery's charge retaining capacity.
If you don't want to junk it yet, reconditioning is the answer to revive and reuse an old laptop battery. So how do you figure out if your own battery can be reconditioned?
Simple! Just see how long it runs on a full charge. If the time till complete discharge is about 1 hour, the battery can be reconditioned.
But if you notice the battery discharging in just a few minutes, then it needs to be replaced.
For more, see
Reconditioned Laptop Battery - Extend the Lifespan of your Li-Ion Battery
