(following from previous dead battery post - but maybe diff. enuf to merit new thread)
Use a hydrometer (I think that's the name of it). My dad has one. It looks like an eye-dropper with 4 colored balls in it. You stick it in the cell, after taking off the vent cover, and draw up enough fluid to more than cover the balls.
Density of the liquid. This directly relates to the ratio of acid vs. water, which directly relates to the amount of charge the cell is capable of producing.
If all 4 balls float (on all 6 cells), then you have a good fully charged battery. If half of the balls float, you have a half-charged battery (could just be drained, or could be incapable of holding a charge). If the balls float on some cells and not others, then the cells they float on are good and the others are not functioning correctly (might just need fluid).
I don't know the answer to this one, sorry. I have heard of topping off with distilled water, though. That needs to be done if water that used to be there has evaporated. A visual inspection to see if the water-acid mixture is high enough to cover the lead terminals. I think the acid, under normal operation anyways, is produced by the reversal of the chemical reaction which is caused by an input of current, rather than a draw, which occurs when the alternator provides a higher voltage, with sufficient current, across the batteries terminals than the battery itself produces.
A single lead-acid cell can produce 2 volts. This is chemistry. A car battery has 6 cells, so that in series 12 volts can be produced.
My dad is an Electrical Engineer and, naturally, enjoys understanding the principles behind various electrical devices. He explained the above (about voltage per cell) to me when my digital voltmeter read 24 volts on a friend's battery I brought home to recharge. It turned out that the 9v battery powering my meter was producing about 4.5 volts. I suspect the meter uses the battery's voltage as a reference, and when that reference was half of what it should have been the battery being measured was reported as double. Replacing the battery in my meter solved the anomaly.
HTH,
-D
other than trying to find the connections between cells, the usual method is to measure the specific gravity of the cell.
Sg, concentration of sulfuric acid = charge state.
Look at the little red and green markings on the hydrometer.
you normally don't, if the battery is in decent shape. However, adding some can help a bit.
Normal voltage on lead-acid cells is 2.0 (1.9 or so is recharge) at low level. Normal float voltage (nominal car voltage) is 2.3 volts (13.8 volts). Charging voltage should not go above about 2.6 volts/cell....
These voltages are approximate.
If your battery is toast, then it will go above 14 to 15 volts and you will draw very little current in charging, one cell (or many of them) will show more than about 2.4 volts (like 3 or 4 volts) on charge...
Hope that this helps a bit
Harvey
Freaky. Another freaky thing is that this newsgroup reply things missed off your signature. Shame. Thanks, tom.
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