Prior to any testing, visually inspect the battery for:
1. Loose or broken connections
2. Cracked or broken case or cover
3. Damaged or leaking terminals
Proceed with the next step if there is no apparent damage on the battery.
Testing the State of Charge:
Take an open circuit voltage reading, using a reliable high quality voltmeter.
Note:  Do not measure the charge level of a recently charged battery, in-vehicle or serviced elsewhere, since the high surface charge will be misleading. To dissipate surface charge, discharge the battery by 15x15 A. If the battery is already installed into vehicle, turn on the front headlights for 15 seconds.  
The Charge Level:
1. If the voltage is around 12.4 (state of charge is 75% or higher), proceed to a load test.
2. If the voltage is below 12.4 (state of charge is below 75%), be sure to charge the battery before a load test in accordance with the charging instructions.
Voltage and density may change by various battery designs.  
Load Testing:
The reading of a load test is largely dependent upon the equipment used for testing. The results should be interpreted in accordance with the instructions provided by the load tester manual. 
Electrical System Check:
Whether you are installing a new battery or working on a defective battery, check the electrical system of the vehicle that utilizes the battery. The most damaging mistake for your vehicle would be over charging or short charging of the battery. Measure alternator output voltage: the reading should be between 13.8-14.4 volts for hybrid batteries (at full throttle); 13.8-14.8 volts for Ca-Ca batteries (in a 12 V vehicle).
Note: In vehicles featuring data storing computer systems, memory loss may occur with changing of the battery. To avoid cutting power to the system, install a second battery or special equipment before dismounting.

1.280 Start-up Electrolyte Level and Charge Status at 27°C

% Approximate Charge  Open Circuit Voltage Approximate Density
100 12.6V 1.280
75 12.4V 1.240
50 12.2V 1.200
25 12.0V 1.160




Note: Disconnecting battery may cause memory loss in electronic systems; to prevent this, the lighter plug can be inserted as an alternative power supply.