[rotorwrench]

When a battery is at full charge, it should have its highest specific gravity with peak acidic content. As a battery gets lower on charge state the specific gravity gets lower too. A portion of the acidic content is held in the in the spongy lead parts of the cell plates. During charging the acidic content comes back out into the electrolyte.

As a battery ages with constant discharge and charge cycles, the water will dehydrate out which will make the electrolyte more acidic in charge state until more distilled water is added. If you add electrolyte instead of water, it will eat the plates up more rapidly.

The lead plates deteriorate from acidic action as well as the added sulfation that happens over time so a battery's life depends on constant use to lower the amount of sulfation over time and careful adjustment of electrolyte so that the plates will have a relatively long life. If it's already sulfated or the plates are deteriorated, then it is close to its end of life. You can try the drain & refill but you need to be sure it is close to fully charged before you drain it. The epsom salts treatment may help the sulfation but there is no way of knowing how much. It's a fair amount of trouble to do all this and it may be beating a dead horse.