Hi Leslie,
When you say the battery is charged, are you actually measuring the voltage across the battery posts? We want to see what the charge is with no charger installed. Just take a voltmeter and measure the voltage of the battery.
My guess is, you have a shorted cell in the battery. If this is the case, the car may not keep running because the alternator cannot provide enough voltage to keep everything running. It needs the battery to provide a stable 12.6 volts in order for it to boost it to around 14.5 - 16 volts. The battery is there to provide a constant voltage source to keep the coils firing and fuel pump running. If this is not there and it drops below 12 volts then the car will just shut off as soon as you take the charger off. The reason it runs with the charger on is because this is providing the vehicle a steady 12 volts.
It is unlikely but you could also has an issue with the alternator. I would recommend replacing the battery with a new one that has a good 12.6 volts and then start the vehicle. Then measure your voltage again across the battery posts and see if it is 14.5 volts. If not, then your alternator being back is the root cause. The alternator cannot keep the battery state of charge up so it slowly drains until it can't even be charged and the new battery will do the same thing.
https://www.2carpros.com/articles/symptoms-of-a-bad-car-battery
https://www.2carpros.com/articles/how-to-check-a-car-alternator
Wednesday, April 24th, 2019 AT 8:27 PM
