Skip the auto shop - Our mechanics make house calls

Q: battery keeps going flat when left overnight

asked by on

to begin with I had a bad alternator as the battery wouldn't hold charge. I changed that and that worked. I've also changed what I thought were bad coil pack and spark plugs. Car was working fine for a while. Now it won't start again will start from jump leads then the alternator charges the battery and car will stop/start all day. Then I leave it for 10+ hours and it won't start again.

My car has 100000 miles.
My car has a manual transmission.

A: You didn't indicate the age of the batt...

You didn't indicate the age of the battery. If the battery is "new" (less than 2.5 years old) and passes a load test, you should check for parasitic loads. With all car accessories off and key out of the ignition, use an ammeter to measure the current flow from battery terminal to heavy battery cable.

What you measure should be in the low milliamps, like 20 to 40 milliamps (varies by car model and whether you have for example a security system), but parasitic load should be very low. If you are measuring a high current draw, that is a problem and will discharge your battery. If your battery is old, it could be self discharging overnight and/or have a bad cell(s). If you'd like help with this diagnosis, a certified technician from YourMechanic can come to your car's location to inspect the battery and perform necessary 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・Save up to 30%

Get a quote

What others are asking

Q: My car won't start back up after idling and won't read codes

With the car idling for an extended period, your engine compartment will get extra hot and this may cause the ignition module to fail, resulting in a stalled engine that will not restart. In order to determine whether the ignition...

Q: Service battery system light? Battery died. CD player has stopped ejecting.

Hi, thanks for writing in. The battery only supplies power to accessories when the engine is not running. As the engine starts, the alternator takes over. So, if the CD player was not working while the engine was running, the...

Q: Battery draining and. Starter motor getting hot

You need to have the battery cables checked to see if they are bad by doing a voltage drop test. If one or both of the cables are bad, it will overheat the starter and not recharge the battery sufficiently....

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...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...