That seems funny at first glance worrying about the acid strength of battery acid. To be honest I don't know. Using rain water is not something I've tried just something I've heard the grey-beards using. I don't go through much more than half a litre a year. I usually put half a bottle in the engine coolant when the contents are turning primordial or use it to clean the toolbox off my hydrometer.
I don't know about the ph concerns nor the purity of ph.
It makes sense though, you can make yellow light by adding red and green or removing blue...not the same thing.
In terms of electrical conductivity, the orange box is the ticket. More MΩ are better.
I have noticed deionised is purer than distilled.
And 14.8V no EQ is for me at least equally effective and less water intense than 14.7V + EQ, also that water loss can be reduced with the watering kit once the hydrocaps are in and the electrolyte is topped off, the float valves shut the gas path and the gases can be recombined if they don't exceed the pressure release valve threshold.
Having said that my golf-carts are pretty much idle the last year. I use 14.8V touring and 14.4V standing idle. I useta have a selection of alternator regs for the season...some were 14.4v some, 14.7v some 15v...I stopped the messin' and realised I was better off chasing current there.
They ought only gas above 14.2V in 25°C
High C-rates are the most taxing, charging especially so. I C3 when I need to and C50 when I can afford to.
After that excessive voltage...overvoltage tends to be more aggressive than overcharge.
Overcharge being overly long charging at the correct voltage...generally a lot better than undercharge and extremely difficult to do. It takes days to overcharge a lead battery at the correct voltage.
