I have a 1984 Toyota Van LE 128,000 original mile. Yes, still running good. Last few years eats batteries, cause is my wife not driving it enough, just sits there. I even bought a solar charger for it, to keep the battery alive. Less than a year old battery acting up again. I charged it up few days ago, next day car would not start, battery is dead. Took it out yesterday, charged it up with my new B&D digital charger, showed 14.1 V. This morning showed 13.2V, took out the acid tester, showed all cells need charging 1.150 gr. Not even close to fair 1.210 gr. Checked the battery in my BMW, showed 1.225gr fair, so the gravity tester works. Why is the charger can show fully charged battery, but the acid tester not? Thx, Julius
Specific gravity will go down as temperature goes up. Just lowering the battery's temperature will increase the specific gravity.
Keep in mind that when you measure voltage, you are measuring potential (volts) but when you measure specific gravity, you are inferring what the voltage will be.
When the battery is fully charged Sp.gr. should show it, not way low. Any way I wouldn't care, but the battery gave me trouble the last month or so.
Thx, got the battery replaced. Kragen hooked it up to the test machine, it showed GOOD battery, fully charged. I showed the sales man the specific gravity is very low, way down in the red on all cells, 1.150, made him convinced the battery is bad. We checked the NEW battery specific gr. needle jumped up, showing it good. Sales man smiled, was convinced too, he said must be some thing wrong with the old battery, not sure what. Only had to pay $13 for the exchange. Julius
Found a good web site explaining battery maintanace.
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Specific Gravity:
The term specific gravity describes the ratio of the density of electrolyte to the density of water. Electrolyte weighing 1.2 times as much as the same volume of water has a specific gravity of 1.200. The full charge gravity of a cell is a matter of design and depends on several factors. The specific gravity must be high enough to contain the amount of sulfuric acid necessary to meet the chemical needs of a cell. If the sulfuric acid content is too high, damage may result to the cell. The standard full charge gravity for lead acid batteries used in an R-E system is 1.250 to 1.285 depending on which type of battery you are using. Since the acid content of the electrolyte decreases linearly as the cell is discharged, the decrease in gravity is directly proportionate to the amount in ampere-hours taken out. The specific gravity at any point in the discharge indicates the depth of discharge, and can be translated into amp hours taken out. A cell having a full charge specific gravity of 1.280 and a final specific gravity of 1.130 has a gravity drop of 150 points.
Example: assume the specific gravity is 1.180 at 77°F at the end of a discharge. That is 100 points specific gravity below the full charge gravity, therefore, 100 ÷ 150g% discharged of rated capacity. So if your battery were rated at 1000 amp hours you would have taken 670 amp hrs out of the battery. Use this formula and the readings from your amp/hr meter to get a good idea as to the battery?s State Of Charge (SOC).
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Specific Gravity During Recharge
The rise of specific gravity is not uniform or proportional to the amount of charge returned in amp/hrs. During the early part of the charge , there is no gassing action to mix the electrolyte with the heavier acid being released from the positive plates. The heavier sulfuric acid will lie on the bottom of the cell container. A hydrometer reading which draws electrolyte from the top of the cell does not indicate the true gravity or actual state of charge. During the gassing portion of the charge the sulfuric acid mixes with the rest of the electrolyte in the upper portion of the cell. The gassing creates a movement upward; drawing heavy acid with it and the specific gravity rises rapidly to full charge value.
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