Is this an ECM problem?

Volts slowly drop to where what quits ,The vehicle stops running ? Is the charge indicator light lit on the instrument cluster /? are any lights lit on the instrument cluster ? The instrument panel cluster (IPC) illuminates the charge indicator and the BATTERY NOT CHARGING message is displayed in the message center when the following occurs:
The engine control module (ECM)/powertrain control module (PCM) detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a serial data message from the ECM/PCM requesting illumination.

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The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a serial data message from the body control module (BCM) indicating the system voltage.

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The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

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The ignition is on, with the engine off

Battery light on ! alternator isn't charging . Test the alternator electrical circuits .Main cable on the back of the alt. should have B+ voltage .Pin # 3 at the connector on the alt. should have B + voltage - fuse F10 10amp under hood fuse box supply's B+ to pin #3 . Pin's 1 & 2 at the connector go to the PCM - engine computer . This is a computer controlled charging system .
Ford PCM controlled alternator testing

the alternator gets power on big wire battery voltage the wire runs to starter, fuse box .alternator fuse goes to automatic shut down relay to relay control in ecm/pcm the field wire comes from ecm /pcm to alt.other field goes back to automatic shut down relay back to charge battery . if not charging at alt. try new alt. and retest.

Check the battery voltage when the vehicle running on idle, it must between 13-15 volt.
Check the battery voltage on full electricity load (turn on headlight, A/C, radio, wiper), it must between 12,6-13,8 V, If the voltage under 12V, check the radiator fan and radio/power amplier

have the alternator bench tested for faulty rectifier diode pack
it may be charging the correct voltage but it is AC voltage and not DC voltage
in which case the battery will die quickly
next to check is the voltage regulator
it has to be 4.5-14.8 volts DC and if it in the ECM unit , will require a new ECM to fix

check 10 amp ECM fuse. Your alternator voltage is regulated by the ECM. If the fuse is good, consider replacing the ECM.

if your not getting juice from your alternator then it is bad the ecm doesnt supply the alt with juice the alt produces its own so if its not producing the correct voltage it will need replaced. it should make 14.75 volts in order to keep your battery fully charged ang to keep up with all running accesories. it should put out no less than 13 volts

First tell me why you don't think it's charging.
Because of the voltage reading you are getting at the battery terminals? The range you want is between 13.6v to 14.2v. The higher the voltage the lower the amps. and true the other way, the lower the voltage the higher the amps. If you get a reading of 13.6v or lower, the alt is nearing or at max output. An alt can only run at maximum for around fifteen minutes and it will start slinging solder from overheating. It's a good indication the battery is either totally dead or junk. Charging above 14.2 the alternater is running wide open and is only putting out high volts which will cause the battery to boil , in turn destroying it. This is a bad alternater. All alternaters have integrated voltage regulater with the exception of ver few of the earlier ones. You cannot test an alternater by removing a battery cable to see if the engine keeps running without taking great risk of damaging the alt, regulator. So tell me why you feel it isn't charging. Remember an alt is not made to charge dead batteries. Their sole function is to maintain the battery charge. Without a battery, the alt won't last 10 seconds.
Hope to hear from you and good luck.

Optomum Alt Charge is 14.5 so yours is Low And Junkyard Electrical Parts I NEVER Recomend I Would Replace Alt w/ Reg. NEW

Rest at ease the 14 volts will not hurt your system idealy your alt will charge at around 14 to 14,5 volts at the alternator and probably have a slightly lower charge rate at your battery at around 14 to 13.5 at the battery this is completely normal