Toyota Prius Gen2 Gen3 12V auxiliary battery drain
The Prius fails to start or shows a red triangle warning due to 12V auxiliary battery failure. Unlike conventional cars, the Prius 12V battery is a small AGM unit that does not receive conventional alternator charging — it is charged by the hybrid system DC-DC converter. The 12V battery typically requires replacement every 3-5 years. Always use the correct AGM specification battery, not a standard flooded lead-acid unit.
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