car battery running flat or car not starting

see also:

• lithium jump start batteries and other jump starters
• 12V batteries and battery boxes
• car over-heating or losing coolant
• oscilloscopes
• multimeters
• Automotive / car maintenance / repair DIY tips
• see also:
  • https://www.youtube.com/watch?v=S3FB8GY2ZyQ how to test your car battery and alternator
  • https://www.youtube.com/watch?v=jdSKlg80DjU how alternators work
  • https://www.youtube.com/watch?v=7eN1gxH6lE4 how start motors work

• car batteries go flat if:
  • you leave a power drain on with the engine not running
    • eg. headlamps, heater or other cigarette lighter device (eg. laptop)
  • the battery is no longer optimally functional
    • it is too old
    • has been run flat too often
    • it is cold (this exacerbates the functioning of an end of life battery or when that is not fully charged)
      • ensure you have all lights, fans and cig. lighter devices turned off before attempting to re-start car
    • there has been too many load situations and not enough car engine running time (eg. frequent starting the car but without ongoing running of the engine)
  • the alternator is not charging the battery
    • check the voltage on the battery terminals when the engine is running - it should be about 14V if it is less than 12V you probably need a new alternator or there is a connection issue
  • there is a short circuit in the system which drains the battery when engine is off
    • see Youtube clip on how to troubleshoot a car short circuit quickly
    • note: a major current drawing short circuit will blow the fuse to that circuit, but smaller current drains will not

• can't turn the ignition key from the LOCK position
  • ensure you have the correct car keys!
  • ensure the gears are in PARK
  • the steering lock has probably been activated:
    • wiggle the steering wheel as you turn the ignition key
  • if the above does not work, ensure you don't have other metal with your ignition key that may be interfering
• can turn ignition key from LOCK but not fully
  • ensure the gears are in PARK and depending on the car, you may need to have the brake on
• can start the engine but it is taking longer than usual
  • this is usually a sign the battery is relatively flat or at end of life
    • try doing a manual full recharge of the battery with reconditioning mode, if this fails to solve the problem, you may need a new battery very soon!
  • it could be the fuel supply may be an issue such as the fuel pump
• can turn ignition key but engine does not turn over
  • check the fuel gauge to ensure the fuel tank is not empty
  • check the internal lights
    • if they don't go on, the battery is totally flat (see below as for flat battery)
    • if they go on, the battery may not be fully flat but lacks charge to start the engine
      • ensure all lights and electrical devices such as fans are turned OFF to reduce load on the battery, then try again, if this fails see below as for flat battery.
  • you may have flooded the petrol engine by switching it off too soon after being started from cold
    • the unburned fuel floods the carburetor, remains in the engine and wets the spark plugs, which prevents ignition and makes the car difficult to re-start
    • when you try to start it, it cranks faster than usual with a whirring sound and there is often a strong smell of petrol in the exhaust
    • remedy to clear the excess petrol:
      • Crank the engine with the accelerator pedal pushed to the floor
      • Continue cranking the engine (for up to 10 seconds) until you hear the engine trying to start
      • Once the engine’s started, allow it to rev up for a second or two, then hold it at a higher than normal idle speed for a few more seconds
      • If the engine doesn’t start within 10 seconds there may be other issues and you should switch off and seek help
  • if you have just driven through deep water you may have a lot of other issues!
    • water entering the air intake will result in water entering the engine and cause a new noise:
      • it can end up rusting parts out like your differential
      • leads to compression issues because there’s no place for the water to go and water is not compressible
      • piston rods will begin to bend and eventually breake which may take a chunk out of our engine on the way out, most likely out of the bottom of the engine, though it could come out the top of the engine, too
      • time to get it towed!!
    • water can easily flow over the transmission and into the vent
      • once water gets in, it dissolves the transmission’s linings and the lubricant begins to fail, resulting in total failure of the transmission
        • if water stays in the transmission for too long, it must be rebuilt entirely
      • water can also damage your car’s transmission by causing the gears to slip
    • salt water in particular will slowly corrode the engine and other parts eventually resulting in failure
    • water may also blow fuses

• check the battery terminals are clean and cables are attached properly
• if you have a multimeter, check the battery voltage to confirm it is indeed flat (it should be at least 12V)
• try jump starting the car
  • if the booster battery is in another car, make sure the car's are not touching each other
  • Turn off unnecessary car lights and accessories
  • using a portable jump starter device
    • these are the safest and easiest approach
    • plug in the jump start cable into the device - see lithium jump start batteries and other jump starters
    • attach the red booster cable to the red +ve of the car's battery terminal
    • attach the black booster cable to the black -ve of the car's battery terminal
    • turn the device on and it should recognize it is in jump start mode and power up the capacitor
    • when the device indicates it is ready, try turning the ignition of the car on
    • you may need to repeat this
  • using another car to jump start your car
    • 1st attach the red booster cable to the red +ve of the car's battery terminal
    • NEXT, attach the other end of the red booster cable to the booster battery's red terminal
    • NEXT, attach the black end of the booster cable to the black neg terminal of the booster battery
    • NEXT, attach the black end of the other end of the booster to the ENGINE's LIFTING BRACKET (NOT the car battery terminal!) or the STRUT MOUNTING NUT or as per vehicle's manual
    • ENSURE the cable is not in danger of moving parts and the clamps are not touching any other metal
    • if using a 2nd car's battery, start that car's engine and run it at moderate idle speed
  • FINALLY, try starting the car with the flat battery then DISCONNECT CABLES in REVERSE ORDER
  • once the engine is running and the jumper cables disconnected, and you have a multimeter, check the battery voltage to confirm the alternator is working (voltage should be around 14V)
• consider replacing the battery unless you know you accidentally left the lights on to flatten it in which case the battery may still be good and just needs a full charge by driving around or via an AC charger
• do a load test on a fully charged battery to see if it needs replacing
  • when you start the car on two attempts, the battery voltage should not drop below 9.6V on either attempt - if it does - probably time for a new battery!
  • see https://www.youtube.com/watch?v=gq0iey9VC94
  • if you decide to charge the battery, remove the black ground cable from the battery first to avoid sending high voltages or currents to sensitive electronics in the car, and take car not to short circuit it!