Re: ro water in wet cell batteries
As I recall that thread mentioned there's a lot of variation in the mineral content of RO water. I've used de-ionized water when distilled wasn't available, and the main point is that there is very low mineral content to upset the battery chemistry.
If your RO water is tested and nearly mineral-free...it beats no water at all, doesn't it?
Long ago I was baffled by mineral readings in water samples, only to find out it just meant the glassware we collected the water in hadn't been rinsed well enough. Trace minerals can come from the "dry" container, as well as the water, so rinse well & often before testing.