If you’ve worked on a Toyota or Lexus hybrid vehicle you’ve probably discovered that if the vehicle hasn’t been run for 30 days or more, the state of charge may gradually decline. To prevent the 12-volt auxiliary battery from becoming discharged, proper maintenance is necessary.

Toyota and Lexus hybrid vehicles are equipped with two types of batteries:

• Hybrid Vehicle (HV) battery
• 12-volt auxiliary battery

If you’re storing the vehicle for 30 days or more: Turn off all lights, accessories and the hybrid system, then disconnect the negative terminal on the auxiliary battery. Hybrid vehicle auxiliary batteries can be damaged by charging at high current rates. If charging is necessary, be sure to use a hybrid auxiliary battery charger because they have microprocessors which vary the rate of charge depending on the battery needs.

• Toyota Technical Service Bulletin TSB-0043-16, found on Toyota’s Technical Information System (TIS), outlines proper handling and charging of hybrid vehicle auxiliary batteries. Special Service Tool (SST) GR8 Battery Diagnostic Station is the Toyota specified battery charger designed for charging auxiliary batteries. If the HV battery is low when the vehicle is running, the gasoline engine will automatically start and the generator will charge the HV battery.

• The 12-volt auxiliary battery will be charged by the HV battery.

If the auxiliary battery is low on charge, you may also use a jump box to READY the vehicle and allow the on-board charging system to restore the auxiliary battery to its ideal charge level.