I have a Jeep Grand Cherokee and when mine doesn't start i either have to jam the shifter forward than start OR while foot is on the brake, turn the key and hold, than shift into neutral, than it will start shift to drive... or reverse and off you goWarrantyWhat did your mechanic say? I am sure he would warranty the job.
If you had him trouble shoot it and you "saved" yourself money by doing it yourself, you may have shot yourself in the foot.
If the alternater or battery were "economy" types, they might be bad from the beginning.
Another thought after the electrical (charging system) is checked. check for a parasitic draw.Draw downI don't know what car you have but on most cars, when the starter is failing, when you crank the car and run it and shut it off, the terminals or posts continue to receive electricity from the battery, meaning that either the starter solenoid is malfunctioning or somewhere along the battery cables, something is draining the battery, check for a stripped wire or have the starter checked, if you have any more questions, Bad alternatora bad alternator that has drained the battery Bad BeltWhen I got a new alternator, I had to buy a new battery. However, the battery kept dying no matter if I kept recharging the battery. I was having the same problems. The car drove good for a day then died again. Found out, the belt was about to break and never was on tightly around the alternator. The belt was not giving the alternator enough power and therefore, the alternator was draining my battery. You should try replacing your belt or the timing belt. After you replace your timing belt and it is on tight and the timing is right, then you should not have any more problems and your car should drive like new!
Only thing that worked for me was to hook up a wire from the back of the alternator (there's a small terminal on the back), then hook up the other end to the positive battery cable (any which way at the post). This is actually to see if the wire that runs a charge from the alternator to the battery is still good. It is usually running attached to the positive battery cable itself. When it is bad, your car will not start because the battery is not being recharged properly. A hard thing to determine otherwise because it is not the alternator or the battery themselves.
WORN STARTER MOTOR
a worn starter motor can drain a battery in a few days especially if the main ignition wire that's connected to the starter motor is not tight enough or the starter motor solenoid is at fault again it will cause a continual drain on your battery I know because it happend to me with my ford mondeo 1.8 TD new battery fitted.
I'm not sure what car you have, new cars are sometimes a sensor while older cars are alot easier to figure out. I would first take the car or the parts to a part store and have them tested. You can always get ahold of a bad batch of either. I had to replace my alternator 4 times and then go to another part store all together before I got a good alternator for it. You could have loose battery cables. If you are able to move the cables by hand then you need to tighten them down this could also make the battery and alternator go bad due to drawing to much juice out of them or even driving down the road and hit a bump then you are broke down on the road. But first have them tested and take it from there checking little things before moving to more expensive parts and harder to install sometimes when alternators go bad they blow a fuse if not changed you can put 20 alternators in must make sure you first have 13.8 - 14.1 volts while car is running