The reason is that sometimes a car battery does not have enough charge inside it to start the engine BUT it often will have enough charge in it to keep the engine running after it has been started by "bump-starting" or "push-starting" the car.
But an auto gearbox does not work like a manual gearbox -
it is impossible to bump-start or push-start a car that has an automatic gearbox!
The only way to start a car engine which has an automatic gearbox is to use a good battery to start the engine.
If your car's alternator is not working you could re-charge your car's battery and then it would start the engine ok, even if the car was an automatic.
Here is what you do:
* first disconnect just the +" lead, or both leads, from the car's electrics * then use a household AC battery charger to charge it up * when it is re-charged you can re-connect the battery to the car's electrics and
* it should start the car ok
Another way to get the engine to start is to use a pair of jump-start leads from a good battery in another car.
To avoid burning cables or even a dangerous car fire
Make SURE you ONLY ever connect
"+" to "+"and "-" to "-"
that is
RED TO RED and BLACK TO BLACK
!!!
And it is a very good idea to keep the other car's engine running all the time, to be sure its alternator keeps its own battery charged up!
But the main problem for you will still be this: if your car's alternator is not working, your battery will keep running down fast whilst you are driving the car.
So it a good idea to get that alternator fixed as soon as possible, otherwise you'll be looking for someone to help you use those jumper start leads every time you have to stop the engine of your car!
As you said in your question, if the alternator is not working, so the battery is not being charged, it is a very good idea to take the positive cable off the battery every time you stop the engine. Doing that every time you stop will prevent the car's other electrics (security alarm, dashboard clock, etc.) from running down the battery whilst you are parked. The longer you are parked the more current will be drained from the battery.
So, if you are not able to re-charge the car's battery somewhere by using a household AC battery charger, always disconnect it from the car's electrics until you get the alternator fixed and your battery is fully charged again.
check the alternator
If your 2001 Jeep Commander randomly stopped working and won't turn on, you likely have one of two problems. Your battery is dead, or your alternator is dead.
Check for poor ground connection either at the alternator or follow the negative cable coming from the battery.
No. If the alternator is working fine, the battery power is not used.
yes if the alternator isnt charging the battery correctly then it couldnt be sending ecu false signals when my alternator was playing up , my central locking my hazards interior light and rear wiper stopped working
CAUTION!!! This may be a problem with the alternator and the charging. Blower fan will stop working if alternator is not charging. You may also see the battery light and brake light staying on as well! Advance Auto Parts or Auto-zone can test your alternator/battery.
Your alternator has either stopped working or is putting out less than 14 volts, therefore not enough charge is getting to your battery.
It depends on what kind of car you are working on, but it sounds like it can be an external voltage regulator, or even a fuse Some vehicles do not charge with out a rpm signal. The cause of the tach not working may also fix the alternator.
It doesn't actually drain the battery, but without a working alternator to recharge the battery it will only discharge as the car is operated.
I had the same problem...the alternator went bad. Both the alternator and battery had to be replaced.
Sounds like an electrical problem, check your battery, alternator, and fuse box, and light wiring.
There is a good chance that your alternator has stopped working. It could also be just a loose wire from the alternator to the battery that is not letting the battery charge. Also it could be a bad battery. When a cell in a battery dies it will hold a charge for a short period of time but then rapidly die. Get the battery checked first. they the wires, then the alternator.