My truck is a 12/05 build with the orginal Motorcraft batteries. I have noticed over the last week it has been taking longer and longer to start. Then today while hooking up a trailer (after starting and stoping it a few times with no long idle time). It wouldn't start. It would crank and crank but no start. Started and stopped a few times then if fired right up. I drove it home with a 10K trailer on and it had power (was towing into the wind). I have the new FICM and run Rotella T6 5W-40 all year round. Fuel Fliters have about 8-9K on them and scheduled for change in November (at next oil change). Is it possible my batteries are just weak? I use Motorcraft cetane improver at every tank and have so since new. I am (hopefully) taking it in to have the batteries tested in the AM. There is some corrosion around the battery terminals and some leakage on the top caps of the batteries. I have no fault lights or codes that I can see.