LM317 voltage regulator R2 is getting very hot? why?

Why can you not just charge a lead acid battery with a constant voltage of 14.1v until the battery reaches the end end of the "top up" charge. I mean, isn't a bulk charge constant current to just speed things up? I mean, u can charge at a constant voltage it will just take much longer? But who cares if it takes longer? I certainly dont?