When the electrolyte is cloudy before it is even attempted to recharge, there is no point in trying to massage it unless it is an absolute end of times emergency.
Any 12v lead acid battery slowly drained over a period of months to anything below 10.5 volts is unlikely to respond to attempts to revive it. Certainly do not rely on any battery which does 'appear' to respond.
Sulfated batteries can be massaged and sometimes massaged quite well given enough time at absorption and EQ voltages, but a 12v battery drained to 6.37 volts over 3 months with cloudy electrolyte, before application of any charge current, is a goner.
They are worth the core charge only, in my opinion.
If the undersized charge wiring to them is not upgraded, I would just get the cheapest 12v battery possible until one can improve the undersized and poorly terminated wiring.
Such systems will chew through any battery quickly, no matter the quality or design, so it is best to view them as disposable until the wiring and terminations are upgraded.
There will be stories about successful battery revival, you tube videos with unsupportable claims, and other delusions regarding lead acid batteries and their magical revival. I do not believe any of them.
Time is the killer. The longer a battery sits under 80% charged, the more its plates will be occluded with sulfates, the more time it rests there the harder those sulfatges become, never to redissolve back into the electrolyte.
When the electrolyte is cloudy and the battery is at half its fully charged voltage and has not yet seen any charge current, it is a goner. I'd not waste any time or electricity trying to refill it.
That balloon was deflated, stepped on, and dipped in tree sap. It will never inflate again.
