Dehumidifier water in battery?

I’m charging some lead acid marine batteries and the instructions say to top off the water levels with distilled water after charging. Fair enough, but I don’t have any distilled water sitting around the place. What I do have, in bucket loads, is water from the cellar dehumidifier. Question: how close to distilled is dehumidifier water?
My thoughts: When distilling, you’re probably dealing with water vapor in the form of steam. When dehumidifying, you’re dealing with water vapor, but also, I would guess, tiny water droplets suspended in air? Which might be capable of transporting trace amounts of minerals? So I’m guessing that condensed water from a dehumidifier would be purer than tap, but maybe harder (from a mineral point of view) than distilled?

If I decide not to use dehumidifier water, how about filtered water from the fridge? It goes through some kind of ion-exchange resin, so I’m guessing that it’s fairly pure. But if they took out all the minerals, it would probably taste crummy. So…fridge filter harder than dehumidifier water which is harder than distilled?

Unless your dehumidifier coils and catchbasin are squeaky clean, there’s undoubtedly crap in there that you don’t want in a battery if you expect it to last. Ion-exchange filtered water can still have mineral content which can poison the battery chemistry. Go to the supermarket and buy a gallon of proper distilled water; it’s only a couple bucks at most.

Agreed - impurities in the electrolyte, even in small quantities, can seriously mess with battery life. Some impurities can produce dangerous results.

Eh? I’m willing to go with reducing the battery life. But dangerous? How? And how much can a low level impurity mess up a battery? Given the large plate area in a standard battery and the very low levels of impurities we’re going to see even in tap water, I confess I have trouble seeing what the big deal would be.

Is picking up a two-dollar bottle of distilled water really that much of a chore?

The issue is not cost. The issue is that while I was looking at the battery and thinking “gosh, I don’t have any distilled water, what would MacGuyver do?”, I had the brilliant idea to use dehumidifier water. Now, I am asking the supposedly knowledgeable folks of the SDMB if this is a hare-brained idea or not. Not because I want to save the two dollars, but because * I want to know the answer *.
Hopefully some knowledgeable person will answer me and back the answer up with facts or informed opinion (e.g. “I work for a battery manufacturer as a chemical engineer and x PPM of ionic contaminents will lower battery life by y%”). Or “I am a chemist and, in an ideal system with clean condensing tubes, a humidifier will produce water that rivals (or doesn’t rival) distilled water in terms of purity.”

I am also interested, but not quite as much, in whether this is a pragmatic solution.

I am totally uninterested in uninformed opinions as to whether this is a good idea – as Cecil says, “I want facts, people.”

MacGuyver would use tap water. Tap water is fine for batteries, unless you live in an area with high mineral content to the water.
Do not use any type of mineral water.

The point is, water from a dehumidifier might not have a low level of impurities - Depends a lot on conditions.

Anyway, in answer to your question - This is a battery that can have electrolyte added, therefore it has a fill mechanism, and therefore, presumably a cap. Even relatively small volumes of gasses produced by reaction with contaminates can build up pressure in the battery case - If the cap pops off unexpectedly, acid spatter is a possibility. And that’s assuming the gasses aren’t flammable. OK, so a small battery isn’t likely to explode like a bomb, but it can still produce a flash, which can be dangerous, too. Either way, we’re talking risk to the eyes. That’s the big deal.