Years ago, I worked with an engineer who had done it himself several times... This was back in the seventies when "Lead Acid" was pretty much it. I will warn you though, if you attempt it you will be buying a new wardrobe of work clothes no matter how careful you think you are! As explained by my mentor back in the day, sulphur deposits and other contaminants collect in the acid solution at the bottom of the cells. This build up of deposits is harmless at first, but becomes a high resistance current bleed into adjacent cells until the cells effectively die. If the structural components of the battery including the lead plates are intact, then the batteries can be emptied, flushed out, re-filled, and re-charged... Easier said then done. If you make it this far, you have two problems... First - what to do with the acid and goop that was remove/flushed from the battery and Second - where do I source the correct solution and strength of Acid to re-fill the batteries... This is where I lost interest back in the day and saved my money for purchasing new batteries. I will tell you though, it did work and the batteries behaved like new ones.
Charlie and Susan 2017 5.0 TA (February 14)
Weight is the enemy... Keep it simple and keep it light !