Two ways to check the charge of a battery.
1.) Open circuit voltage
Use a voltmeter to measure the open circuit voltage of the battery (see chart below for state of charge). Open circuit voltage is the voltage of the battery with no load or disconnected from any circuit.
For a flooded lead-acid battery you should see 12.6 to 12.7 for 100% charged, 12.4 for 75%, 12.2 for 50%, 12.0 for 25%, 11.9 for 0%.
2.)
Use a hydrometer to check the density of the battery's electrolyte, assuming you have a non maintenance free battery that has the removable caps for each cell.
A hydrometer is used to test the state of charge of a battery cell. This is performed by measuring the density of the electrolyte, which is accomplished by measuring the specific gravity of the electrolyte. The greater the concentration of sulfuric acid, the more dense the electrolyte becomes. The higher the density, the higher the state of charge.
Hydrometers are a cheap way to measure both the charge state and health of flooded batteries and only cost $8.99 at Canadian Tire.
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Topic: Battery recharge time? (Read 2717 times)