Skip the auto shop - Our mechanics make house calls

Q: Brand new battery keeps being drained. I found the interior light switch does not work. Could this be the culprit?

asked by on

Bought the car used. Has brand new battery. Keeps being drained and car won't start if not driven for greater than 16 hrs. No problem was disclosed. Already checked all the fuses and removed the fuse for the cigeratte lighter that looked bad. So frustrating as I really can't afford a fishing expedition at a dealership.

My car has 137000 miles.
My car has an automatic transmission.

Even though you have a "new" battery, it does have to be load tested just to be sure. Such is not a problem though as many large battery vendors will do it for free. Once you have confirmed the battery, you want to check the output of the alternator and compare against the Factory Service Manual (typically output should be around 13.8 to 14.5 volts but the FSM spec is the one to rely on). If all that checks out, you have a phantom load on one of the car’s circuits that is drawing a significant amount of current when the car is off. Normally, some battery power is required to keep the car "alive" when it is sitting in your garage (alarm, computer, clock, etc.) but this current draw is so small, at around 50 milliamps, that it won’t discharge the battery "quickly". Basically, to find the phantom load(s), when the car is off, you measure the amp draw from the battery to each and every circuit fed by the battery. If you do this methodically, eventually the circuit that is discharging the battery will show up. That individual circuit(s) is then traced to identify the faulty device and or wiring issue that is letting current flow when it should not flow.

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
  1. Home
  2. Questions
  3. Brand new battery keeps being drained. I found the interior light switch does not work. Could this be the culprit?

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: Car has no power

Hello. This can be caused by a number of things. Most of the time it is caused by the timing belt being worn out causing the timing to be slightly off. This is enough to affect the power of the...

Q: Are the powertrain control modules in a 2004 Dodge Ram and 2008 Dodge Ram the same?

The powertrain control module (PCM) part numbers for the 2004 and 2008 model year trucks are different. So, it's possible that the PCM could be the problem. However, there are countless things that could have gone wrong with an engine...

Q: Car not stopping when I press brake pedal.

I believe you may have a problem with your master cylinder. I would suggest first having the brake fluid flushed if it is dark. If that doesn't fix it then most likely the master cylinder is bad. I would have...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...