How do you find the specific gravity of battery?

Answer 1

'Lead-acid' batteries, sometimes called 'wet' batteries, have lead plates and liquid

sulfuric acid inside. As a cell charges up, the specific gravity of the acid increases,

and as it discharges, the specific gravity of the acid decreases. So, measuring the

specific gravity of the liquid in the cell is a quick and easy way to tell how fully

charged the cell is.

Anybody who owns and uses some 'wet' batteries also owns a hydrometer ... a

gadget that measures the specific gravity (or density) of liquids. The most familiar

type looks like a turkey baster, with a little glass glob inside that looks like a

miniature thermometer and has numbers marked on it. To use this hydrometer, you

squeeze the rubber bulb on top, stick the snout into a liquid, release the rubber

bulb which draws some of the liquid up inside, and the little mini-thermometer

inside floats in the liquid ... part of it above the surface and part of it below.

The higher the specific gravity of the liquid is, the higher this little thing floats.

So you look in on it, and read the number marked on it right at the surface of the

liquid, and that's the specific gravity.

If you're doing this, then you know what number you want to see, and you know

whether the number you see means charged, discharged, or something in between.

As I recall back in the day, I used to see specific gravity somewhere around 1.20 - 1.25

in each cell of a 48-v battery that was properly floated and equalized on its rectifier.

But to be honest, that was a while ago. The constants of nature that define the

elementary charge and the Atomic Mass Unit could well have changed since then.