Hybrid Electric Vehicle Training Educator

12-Volt Battery


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The 12-volt battery, also known as the low-voltage battery, supplies power to all the low-voltage systems on the vehicle, such as the radio, lights, instrument cluster, horn, and turn signals. All onboard computers use the 12-volt power to operate properly. The battery stores energy in a chemical form until it is need by the rest of the vehicle's low-voltage systems. As the battery's chemical energy is used, it starts to discharge and must be recharged by the vehicle's charging system.

The 12-volt battery is located inside the vehicle on this hybrid model, so it is necessary to use a specially designed battery to help prevent it from venting hydrogen gas inside the vehicle. This is also true of any nonhybrid vehicle that has a 12-volt battery inside the passenger compartment. The battery is made up of a Glass Mat design. The lead acid electrolyte consists of a mixture of sulfuric acid (in its diluted form) that is mixed with water. The mixture is 36% sulfuric acid to 64% water. When the battery is fully charged, the 36/64 mixture is outside the Glass Mat. As the battery becomes fully discharged a percentage of the sulfuric acid enters the Glass Mat, leaving only water outside the Glass Mat cells.

© 2012 National Alternative Fuels Training Consortium.

12-Volt Battery

12-Volt Battery