Check the Battery Health

• Start with inspecting the health of the battery. Modern car batteries typically last between 3-5 years. If your battery is more than three years old, it might be time for a replacement.
• Use a multimeter to check the voltage of the battery. A fully charged car battery should read about 12.6 volts when the car is Off and around 13.7 to 14.7 volts when the car is running.
• Consider having a professional conduct a load test to determine if the battery holds charge properly under stress.

Inspect for Parasitic Draw

• Ensure that no accessories, lights, or electronics are left on when the vehicle is turned off. Items such as cabin lights and seat heaters can contribute to battery drain.
• Remove one of the battery terminals and set your multimeter to measure current in amps. Connect the multimeter between the battery post and the removed cable to detect any excessive current draw (>50mA in sleep mode).
• Identify the circuit causing the drain by removing and reinstalling the fuses one at a time while monitoring the current draw on the multimeter.

Update or Reset Software

• Cars like the 2015 Lexus LS460 have multiple computer systems controlling various functions. Over time, software bugs or corrupt data can cause irregular behaviors, including battery drain.
• Visit a Lexus dealer to have the car's software checked and updated to the latest version.
• Resetting the system via a battery disconnect might also help. Remove both battery terminals and hold them together for about 10-15 seconds to discharge capacitors and clear stored energy. Reconnect the battery and see if the issue persists.

Check Alternator and Charging System

• The alternator is responsible for charging the battery while the car is running. A failing alternator may not charge the battery adequately, leading to drain issues.
• Using a multimeter, check the voltage at the battery terminals with the engine running. If the voltage is outside the 13.7 to 14.7 volts range, the alternator or voltage regulator could be defective and might necessitate replacement.

Ensure Proper Electrical Grounding

• Check the main electrical grounds from the battery to the chassis and from the engine to the chassis. Loose or corroded ground wires can lead to poor electrical performance and battery drain.
• Clean any corrosion with a wire brush and ensure all ground connections are tight and free of rust or debris.

Examine the Keyless Entry System

• Some Lexus LS460 models equipped with keyless entry systems can experience battery drain if the fob is continuously trying to communicate with the car.
• Keep the key fob at a sufficient distance from the vehicle when not in use to prevent unwanted communication.
• If necessary, visit a dealer to have the keyless entry system checked for faults.

Look for TSBs (Technical Service Bulletins)

• Lexus regularly issues Technical Service Bulletins to address known issues with their vehicles. Sometimes, these bulletins include recalls or fixes for battery drain problems.
• Check with your local Lexus dealer or visit the Lexus website to see if there are any TSBs pertinent to your 2015 LS460.