For charging Seal Lead Acid Batteries
Their are two options 1) Fast charging method will take 5 - 6 hours and needs complicated circuit because of the charging method. 2) Float charging method will take upto 16 hours and most commonly used ,for float type charging apply 2.25 V to each cell i.e.. for a 12V battery which have total 6 cells you will need 6 * 2.25 = 13.5V.Apply regulated 13.5 VDC to your battery for about 16 hours assuming its already discharged upto 70% of its total capacity.
Good Luck