Over-voltage is required (you can trace that to thermodynamics) - but there's a caveat or two you need to heed: The higher the current supplied, the faster the battery will charge, and also, the hotter it will get. That is also a factor in reducing the life of a rechargeable batter. When fully charged, it is best to reduce the charging current to none, or better still, remove it from the charging state. This, too, will mess up your battery life. <modify> I noted well down the thread that you identified this as a lead-acid battery. A point to note about this is to consider that a car's lead-acid batteries are charged by the alternator but the voltage regulator keeps if from overcharging by shunting away the current through a power resister (as heat) when the voltage indicates it's fully charged.
"The difference between genius and stupidity is that genius has its limits." - Albert Einstein
"As far as we know, our computer has never had an undetected error." - Weisert
"If you are searching for perfection in others, then you seek disappointment. If you are seek perfection in yourself, then you will find failure." - Balboos HaGadol Mar 2010