Battery Specific Gravity
Battery Specific Gravity
Find out about the specific gravity of lead acid battery electrolyte
storageIt is possible to test the state of charge of a
lead acid battery (or
battery bank) with a multimeter simply by measuring the voltage however this is not always an accurate indicator. More accuracy is provided by measuring the
specific gravity of the
electrolyte in the battery (assuming that the battery is not of the sealed type).
Measuring the Specific Gravity of a Battery
Specific gravity is measured with a
hydrometer. Simply draw the battery acid into the hydrometer so that the float is not touching the sides, top or bottom of the barrel. Take the reading with your eyes level with the surface of the drawn up liquid, and then
subtract 0.004 for each 5°C above or below 25°C. Do this for each of the cells of the battery.
Below is a table of the
specific gravity measurements to be expected at 75°F.
| State of Charge | Specific Gravity |
| 100% charged | 1.265 |
| 75% charged | 1.239 |
| 50% charged | 1.200 |
| 25% charged | 1.170 |
| Fully discharged | 1.110 |
Buy a Hydrometer
Hydrometers are available from many
home brewing suppliers but may not be suitable for measuring battery electrolyte - you need to find one with a
specific gravity range of approximately 1.000 to 1.300. Take a look on
eBay UK where the search
battery hydrometer usually brings up a good selection of suitable hydrometers.
Article Last Modified: 15:13, 19th Aug 2008
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