Battery drains when driving, starter replaced alternator checked ok

Don't change the starter. I'd recommend a parasitic drain test. parasitic draw test YouTube

You may need to check your regulator,

I would have your altinator checked and make sure it is putting out at least 13.5 volts at the battery while running if not the check your wires to the starter from the battery and if ok replace the alternator.

If your alternator and starter is good. You might have a dead cell in your battery, If your battery checks ok, then you have a bad ground= corroded or broken wire.

drive belt tension
have the voltage regulator checked /replaced
if it is faulty the battery will drain as it is running all of the electronics without help from a alternator
AS the ecm draws a lot of current, a battery not charging will not last long
most modern cars run about 85% of the alternator with the rest for charging the battery
if the voltage regulator is part of the ECM, replace the ecm unit

CHECK ALTERNATOR OUT PUT SHOULD BE 13.5 VOLTS TO 14.5 VOLTS.IF NOT ALTERNATOR IS NOT CHARGING BATTERY.CHECK ALTERNATOR FUSE AND CHECK ALTERNATOR POSITIVE FEED WIRE AND VOLTAGE REGULATOR WIRES.IF ALL IS GOOD ALTERNATOR NEED TESTING AND REPLACED.IF ALTERNATOR GOOD BATTERY CABLES COULD BE OLD CAUSING POOR GROUND AND HIGH RESISTANCE IN POSITIVE CIRCUIT. STARTER SOLENOID FAULTY IF NOT BEEN REPLACED.

DID U CHECK THE STARTER TO SEE IF IT IS GOOD!!!MAKE SURE THE WIRE IS CONNECTED REAL GOOD TO THE STARTER TOO!!! B/C IT WILL DRAIN YOUR BATTERY!!! THE SAME WITH THE ALTERNATOR IT TOO WILL DRAIN YOUR BATTERY!!

Have you had your Battery,starter and alternator checked? if starter or alternator bad will drain battery. If battery is bad will damage alternator over period of time. If not changed. Also check your battery cables, make sure your +/- is without corrosion. Possible voltage regulator.Hope this helps..
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Tricky ... Was the alternator replaced with a 2nd hand one or a new one?

A defective alternator can allow the battery to discharge within a few minutes (the diodes in the rear of the alternator can burn out and cause the problem. The diode pack can be replaced). When this happens recharging the battery only replaces the power in the battery - which drains straight back to earth via the alternator, flattening the battery again - often within a couple of minutes or less.

Does the battery lose its charge when the car is standing or just when the engine is fired up?
If the battery loses its charge overnight, try disconnecting the wiring from the rear of the alternator (also look at the electrical connector that fits into the back of the alternator - look for melting/burning marks which suggest something may be amiss inside the alternator).

Let the car stand overnight with the alternator wires disconnected. Will it start up ok and drive (with the alternator wires still disconnected) the next morning?

You could also try just disconnecting the alternator wires, firing up the car and then driving it -
If the car drives ok without dying out and gets further down the street than it usually does, then it probably is the alternator at fault. The car should drive until the battery drains and has insufficient power to trigger the ignition. You certainly would get further down the street with a charged battery and disconnected alternator than you currently do.

It does sound as though you've had an alternator fault to begin with. If it has been replaced with a 2nd hand unit that unit may also be faulty. Rather than replace parts in desperation, visit an auto electrician's - within a few minutes they will be able to test the battery/alternator output and also identify where the lost current is going. It will be cheaper in the long run to have an auto electrician look at the charging system. It only takes a few minutes.