Is there an alternative to this for battery top-up? Have heard boiled water left to cool does the same job?

Boiling water and collecting the evaporated / cooled steam is distilling, same as what you would get in bottled water. It will not remove the mineral ions ie. de-ionise the water.

 

To be honest though, i don't know if you can use distilled water in the battery.

De-ionised water is the same as distilled water (not boiled water)

umm, distilled is not de-ionized, distilled is actually purer than normal de-ionized water, as distilled removed all components from the water, not just removing the ions

I aint sure but you could always get the tablets that you put into distilled/de-ironised water they give an old battery a new lease of life..........apparently?

Boiling water and collecting the evaporated / cooled steam is distilling, same as what you would get in bottled water. It will not remove the mineral ions ie. de-ionise the water.

 

To be honest though, i don't know if you can use distilled water in the battery.

 

Ye a slower way, also used as a survival technique for getting clean water from sea water or other undrinkable source... even urine. Get two bottles, idealy one transparent, fill the transparent one with water then join the two together at the neck. Then position them so that the one with water in it is in the sun (so it heats up) and the other kept cool in the shade or covered and angled so that water will collect in the bottom. The heat causes evaporation of water in the filled bottle which then condenses in the cooler bottle and collects as distilled water in the bottom of the bottle.

Ice/frost out of the fridge/freezer is effectively distilled water once melted too.