How to tell your laptop charger is faulty:
When your charger is plugged into the charging socket it states battery power and does not show ac power and charging. Even if you laptop charger pack has its lights on it can still be faulty. The easiest way to test is to plug the charger into a Voltage meter and check the Voltage output is the same as it states on your charger if its less or showing mili amps then it has failed. Often they can still light up and the problem is a frayed cable or charger pin connector fault. Many laptop users move there cable about in the socket to try and get a connection, if you do this often it is bad as what should have been a simple laptop charger replacement turns out into needing a new notebook charger and a new motherboard charger pin socket. Which depending on model of laptop can be a 3-5 hour strip down and pin re solder or power socket replacement. Laptop AC adapter sockets do not like to be force in one direction and eventually break free from motherboard. So replace your laptop charger as soon as it stops working every time it is plugged into your laptop.
Cheap clone and copy chargers can run extremely warm and cause the charger socket to melt, this is common place with cheaply imported chargers and an immediate fix for this is to replace your charger with a genuine laptop charger.
Check the Voltage is correct on your charger. Underneath your laptop, notebook or netbook it will state an input match this to the correct charger output. Voltages have to be the same, amps can be the same or higher. So for example of you have a dell laptop charger that is 19.5v 3.34a but you Dell laptop states it needs a 19.5V 4.62A charger majority of the time the laptop will tell you it has a lower charger fitted and it will not charge the battery. Other models such as Acer laptops do not normally tell you this but will simply either not charge or take a long time to charge or will only charge when the ac adapter is plugged in and your laptop is turned off.
Check the pin size is correct. Only a few manufacturers have the same Voltage amp and model number of there chargers but with 2 different pin sizes. Acer the most common to do this. Acers 4 most common laptop chargers are the Acer 19V 4.74A charger and the Acer 19V 3.42A charger both come in 2 pin sizes the 2.5mm and 1.7mm. The correct way you measure this is with a tape measure or ruler and check the diameter of the hole of your old Acer laptop charger. This is important as often people will use a 2.5mm on a 1.7mm laptop and it works in a fashion often by forcing into place this can cause extra heat around the pin which can again break your Acer laptop charger socket or even melt the plastic surrounds. So do check this.