Technician Handbook 601 Hybrid Systems for Collision Repair Auxiliary Battery Service Hybrid vehicles use a 12-volt auxiliary battery to power the ECUs and other 12-volt components. Most hybrids use a sealed Absorbed Glass Mat (AGM) battery. In an AGM battery, the electrolyte is trapped in separators to reduce the amount of hydrogen gas released when the battery is charged. An AGM battery should never be replaced with a conventional lead-acid battery. Charging During normal operation, the 12-volt battery is charged via the DC-DC converter, and the charge rate is kept low to prevent early deterioration.
When charging the auxiliary battery from an external source, always use a slow charger to protect the battery. Jump Starting If a hybrid vehicle’s 12-volt battery is depleted, the vehicle can be jump started like any conventional vehicle. Because the 12-volt battery on most hybrid vehicles is not located under the hood, a jump start terminal is provided for easy connection. When using the jump start terminal, connect the positive (red) cable to the jump start terminal, and the negative (black) cable to the frame. Reversing the polarity can blow the 100-amp fuse.
Testing Do not attempt to test the auxiliary battery by connecting to the jump start terminal, because the wiring between the jump start terminal and the battery will affect the test results. Connect the tester directly to the battery terminals for accurate results. NOTE Many components must be reinitialized or calibrated after 12-volt power has been interrupted. These components vary based on model. Most repair manuals include an “Initialization” section that lists the necessary procedures. 16 Collision Repair & Refinish Training