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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.
Download the STMicroelectronics datasheet of LM317 ,in their you will find a circuit for 12V battery charger or else you can search in google for 13.5 VDC power supply circuit.Anyway if you use LM317 voltage regulator,remember its a linear regulator if the difference between the input voltage with the output is too big then you will loose a lot of power in form of heat.You can use switching regulators but that will be a bit complex.