Battery keeps dying for no apparent reason

ANSWER : Hello. If the battery and alternator are fine then I would test the ignition switch. It will commonly stay on and cause this. If it is fine, then an amperage draw test needs to be done on the vehicle. If all of the electronics are stock, then the issue may be a sticking relay. I have had the main fuse box fail internally and cause this a few times on this vehicle and the amperage draw test will identify this as the issue. If you need to have this looked at, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose your battery.

ANSWER : There are three possibilities, to start with: 1) there is a voltage drop in the wiring between the alternator and the battery; 2) the "parasitic" power draw occurs while the car is running, not so much while it is off, thus overwhelming the alternator and consequently the battery is not being fully re-charged; 3) there is a parasitic power draw when the car is off but to pick it up requires data logging. With regard to these possibilities, if you desire that the required diagnostic steps be performed by a certified mechanic, please simply request an electrical circuit/charging system diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

ANSWER : Hello. It is possible that the your 2003 Lexus SC430’s computer is draining the battery during the time that it is not being driven. It is never a good idea to let a car sit for extended periods of time without the engine being run or driven.

If this problem only happens after the car has been sitting for a week or so, this may be caused by something else. Running the engine or driving the car may solve the problem. If it does not, it is also possible that there is a problem with the electric/charging system of your car. If the alternator is faulty and overcharging the battery, it may cause the battery to lose its charge faster than it should. Have a certified technician, like one from YourMechanic, come and complete an inspection of the electric system in order to properly diagnose your problem and make the necessary repair.

ANSWER : Batteries that drain overnight are common. Usually when this occurs, there is a parasitic drain on one of the car’s systems. When this occurs it drains the battery down over time. Batteries that are drained down repeatedly can cause them to fail. The most common causes of the battery drain are aftermarket accessories, radio, power windows and seat motors. If you can find the cause of the parasitic drain, a certified mobile technician from YourMechanic can come to your car’s location to diagnose your battery and determine what should be done.

ANSWER : This may be a sign of a failing voltage regulator or potentially a bad grounding problem causing a draw on the system. The voltage regulator is a unit that regulates the charging of the battery by the alternator. Often times this will result in the alternator allowing too much power to be delivered to the battery resulting in damaging wires and prematurely sometimes destroying the battery. In other cases it may result in the alternator not supplying enough power to the battery, resulting in undercharging the battery or not charging it at all. In either case, I would recommend having an expert from YourMechanic come to your location to diagnose your vehicle’s charging system.

ANSWER : Hi there. It is possible that a charging wire running from the alternator to the battery that is damaged and needs to be replaced. If the alternator was tested and was good, then it’s possible that you have a stuck electrical relay that is causing what’s known as a parasitic battery drain. This would not explain the noise however, so it might be a good idea to have a professional mechanic complete a car is making a noise inspection to determine what is causing this noise and if it’s related to the battery issue somehow.

ANSWER : It sounds like the alternator is not charging the battery, when are you driving long distances. Running all the accessories and then shutting it off can cause the battery to be too weak to restart the car. If the alternator is intermittently not charging, then you may have other wiring issues or just an intermittent problem within the alternator. Have the charging system checked by a mechanic after driving it and not shutting it off, to see if the battery is being charged. You may also have a body control module issue with extended storage mode. The dealer can check this mode with the special scanner and checking the extended storage fuse is not installed.

ANSWER : The problem is not the battery, but the charging system is not keeping the battery recharged. The alternator is the most common cause of this, though failing battery cables can also be a cause. I would recommend having the battery cables and alternator tested and checked by a mechanic, like one from YourMechanic, who will come to you and diagnose the problem for you. Do not try and drive it or it will leave you stranded from the battery going dead again. The cables to the battery from the alternator may be bad or the alternator is not charging. Only the testing and diagnosis will reveal the problem.