Reviving old batteries?

I looked into this subject also since I have a battery back up sump pump. The thing with the Epsom salt and also baking soda made no sense at all. The plates in mine are still immersed so??? I also thought about buying the battery acid solution and using that to rejuvenate the battery. Stuff can be had at a couple of local hardware stores relatively cheap. To replace the deep cycle battery is something around $150 since it has to last 7 hours? And cashola is real tight here at the moment.