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 battery....

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: 2000 Lexus GS400 has new battery, but will not start

Hello. Thanks for writing in about your 2000 Lexus GS400. There are various reasons for a car not to start. The best way to determine what component is causing this is by having a technician scan the VSC (vehicle stability...

Q: Replaced battery got another jump from AAA won't start, service b1 shows on dash which I know I need oil change but is that why?

Hello There, The B1 service in your Honda Accord indicates the need for the oil change service and tire rotation as you know. This service does not have anything to do with the battery or the vehicle not starting. If...

Q: Alternator not working right

An alternator can malfunction in a lot of ways. It can provide too much or too little voltage, not enough current, no current or the wrong kind of current. The wrong kind would be AC voltage instead of DC. Once...

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...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
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...