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.

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・Fair and transparent pricing

Get a quote

What others are asking

Q: Car wont start

There are a couple of issues at play here. If the engine turns over, then this indicates your starter and battery are both working properly. The next question would be whether or not the engine is getting spark and fuel....

Q: My battery does not charge. It keeps on drawing power when I switch on the head lights, spot lights, and noise from the dashboard

Hi, thanks for writing in. If your battery is not charging properly and you are having other electronic issues with your vehicle, it is likely that your alternator may have failed. When your alternator fails that can cause lots of...

Q: Won't start after warmed up.

Hello. If the vehicle starts after being allowed to sit for a while, then it may be possible that the issue is heat-related and goes away once the car cools down. If the vehicle will start with starting fluid, then...

Related articles

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...