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Ilan SHapiro

I use this for my battery fluid regularly

William Murdoch

My kit cost a bit over US$100 when I bought it a few years ago, but I see there are refractometers on Amazon for $20. Anyone have any idea if the cheap ones are reliable?”

I’m in a nice position to give you one data point. In the past I have used the WalMart pink stuff to protect my drinking water system on my boat in NC from freezing. One of Drew Frye’s articles on antifreeze left me wondering what was in it, and I changed to USP propylene glycol. Tractor Supply keeps it to treat cattle with tummy aches. I bought a gallon early this week. (At $50 rather than the past $20, I may not do that again.) I also have an Amazon refractometer calibrated in %EG, %PG, and battery sg. I bought it Dec 29, 2020. It now sells for $20.99.

Using the dropper pipette in the refractometer’s case, I added 2ml water and 2ml PG to a shot glass, stirred it, and twice measured the %PG of the mixture and of my tap water. The water was 1%PG both times, and the mixture was 54%PG both times.

The instructions tell how to zero the instrument, but I am not to be bothered over a 1% difference. I also am too lazy to change volume% to weight% which may explain the difference in the mixture. I think the refractometer is fit for the purpose of gauging the freezing point of the residual water in my drinking water system.

My refractometer looks a lot like yours.