Weak supply side voltage is the #1 reason for FICM failure. The official Ford spec indicates that during cranking operations, voltage is not to drop to 9.3 volts for more than 10 seconds. Letting batteries dip below 10.0 volts shouldn't ever be tolerated in actuality. Fully charged batteries left sitting overnight should measure 12.7 volts or maybe a bit more. If you are seeing numbers below 12.5, it's time to get those batteries on a charger! We recommend a good desulphating charger like is offered in the Battery Tender and BatteryMINDER line of products, though any smart charger will do.