Skip the auto shop - Our mechanics make house calls

Q: My batteries keep draining down

asked by on

My batteries are both good and the alternator is good but my batteries keep running down. It will start sometime and other times the truck will not start.

My car has 116342 miles.
My car has an automatic transmission.

A: Hi there. Assuming both batteries are good,...

Hi there. Assuming both batteries are good, the alternator is properly charging. This would lead me to believe there is a parasitic draw on the batteries. This draw must be excessive to run down both batteries.

You could attempt to isolate the draw. Disconnect both negative battery terminals, install a test light inline between the negative battery post and battery cable terminal end on one battery. If the test light is brightly lit, then a draw is present.

Remove and reinstall fuse(s) and relay(s) one at a time until test light dims or goes out. Whichever fuse or relay is disconnected, dims, or causes the test light to go out is the circuit drawing on the batteries.

If the short or component drawing cannot be isolated, or you need further help, I recommend having a certified technician, like one from YourMechanic, come to your car’s location to diagnose the battery drain and guide you through repairs.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Truck starts then immediately dies

Hello, thanks for writing in. Most of the time this is caused by a fuel system issue. I would usually start by installing a scan tool to see if there are any codes in the computer pertaining to this problem....

Q: Alternator not grounding on 2000 BMW 323Ci

Hello. If this occurred right after the accident, then I would check the ground connections on the battery first. If they are fine, then the wire going from the battery to the alternator needs to have a voltage drop test...

Q: Truck trembling when starting.

These symptoms point towards fuel delivery, Have a certified mechanic test your fuel pressure I have a feeling it would be out of specification. Most port fuel injection systems run at about 35-50 psi depending on make and model and...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...