making battery charger for lead acid battery 6v
If it's a 4.5 Ah capacity battery, then it's 4500 mAh--not a 9000 mAh capacity battery.  You should search online for how to properly charge a LA battery.  Battery University will provide you with all of the info that you need.

re:  "...you can charge a lead acid battery by just connecting it to a voltage supply equivalent to what its voltage would be if it was fully charged and wait till the amperage pulled approaches 0"
You are not completely correct.  It is possible to build a charger that will provide too much charge current.  To be safe, you should also ensure the charge current is limited to what the battery spec sheet specifies.  You should also follow all safety precautions when charging LA batteries as hydrogen gas is explosive if not managed properly.

re: "is this battery dead or can it be recharged and brought back to its previous state?"  You will have to charge it properly to answer that question.  If it hasn't been suflated for too long, it might be possible to restore the batt.