I have a dead Li-ion battery from a Wifi device. Since I didn't use it for a couple of months, Its dead now. I have read somewhere that boost charging is used to charge and bring the battery back to its original capacity. How much volts and current should I supply to bring it back to life?
You can't "boost charge" a Li-Ion battery. When you say it is "dead", I assume it doesn't deliver any voltage/current. There could be two scenarios of what has happened.
The battery has a built-in protection circuit. When the (internal) cell voltage drops below certain threshold (like 2.5-2.9V), the circutrty disables the battery output.
The cell gets drained to actual zero due to self-dicharge parasitics. Then it is formally "dead".
There is a third scenario when the cell went dead after a catastrophic overdischarge (short), which destroyed internal conductors. I assume this is not the case here.
In first two cases there is a chance for recovery. You should apply a very modest "precharge" current (say, 100 mA). If the cell is just overdischarged and is shut down due to protection, it will quickly gain some voltage above the cut-off thershold, and the protection circuit will disengage. Then you charge the battery using normal means of your device.
If the cell has no protection and is dead by electrochemical depletion, there is still a chance that it will come back to life. However, studies show that the process of recovery is unpredictable, and in no case the cell can be restored to its original capacity. The result can be anywhere. See also some relevant discussion here.
Try do a couple of charge / discharge cycles. First charge up to 4.1 V then use a power led or a power resistor like 10 ohms for discharge until the battery reaches 1.2 volts. Then do the same thing more 2 times. Usually, it works for me.
Also, Check this article. It may help you. http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries