Chrysler Repair: town & country battery drains

Question
my mothers van wouldnt start. gave it a jump it starts. then it doesnt overnight. my thoughtr was the alternator. took to auto place for code reading they said alternator not good.
here is where big brother steps in and says it may be the ECM so how do i check that

Answer
Hi Cathy,
If the repair shop did a fault code check and identified the alternator as the problem then I would believe that if you saw them do the fault code check or test the alternator. The other thing you can do is drive it and look at the battery voltage gauge on the cluster and see where the needle is pointing toward and also look at the warning light for the battery which should to be "on" when you first turn the key to the 'run' position but have not yet tried the starter. If after you start the engine that battery light is still 'on' or glowing even dimly then that would corroborate the charging system (alternator) is not putting out the necessary voltage to maintain the charge on the battery.
The ecm idea would need to be corroborated by a fault code readout that pointed toward the ecm, so I wouldn't go down that path without a confirmatory code that it is faulty. It is too expensive to just guess that the ecm is the problem.
Let me know what you observe and tell me the year and engine size (L) of the minivan if you send a follow-up question.
Please read the PS (below) and respond to it.
Thanks for doing that.
Roland