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some one pointed out to me that there is a better and more accurate way, as he says, to measure the specific gravity of my lead-acid battery then the simple hydrometer. he suggested some thing like this.

is this actually better? has someone tried it and can give some insight about this tool?

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up vote 3 down vote accepted

A refractometer is actually a much more accurate tool for measuring specific gravity (of any liquid). Though IMO the accuracy of a hydrometer is close enough as to not justify the additional expense.

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But i do have an hydrometer and the measure is so not accurate... the curve of the liquid is messing up the reading and also the tilt of the float is annoying. maybe it's just my hydrometer but i think that the range of accuracy is about 0.015, and in lead-acid battery it's alot! – Asaf Chertkoff Mar 20 '11 at 15:18
The float is annoying - I'll abslutely give you that. The cusp of the liquid being large enough to throw off a reading is probably related to the hydrometer used. I do own a refractometer and that's what I use - but like I said ... there is a considerable cost difference. It does depend on just how accurate you need a reading (even in a lead acid battery a difference of .015 won't make a gigantic difference -- the difference between a charged and discharged battery is about .15) – iivel Mar 20 '11 at 15:29
oops. that what i meant, 0.15 :) – Asaf Chertkoff Mar 20 '11 at 15:59
Ok. If your hydrometer has an accuracy of .15 you will want to look at a replacement anyway. You may have better luck with a needle or ball type hydrometer than your float hydrometer. – iivel Mar 20 '11 at 16:04
I use refractometers for brewing beer all the time and it is very accurate. Much more accurate than the hydrometer we use – Joe Philllips Mar 21 '11 at 22:18

Use a digital density meter. You can get portable ones with an accuracy to 0.001 g/cm3 and a repeatability to 0.0005g/cm3. Try here: http://www.anton-paar.com/Portable-Density-Meter-DMA-35/Density-Meter/60_UK_en?product_id=325

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