First off I just joined the group although Ive lurked for quite awhile. Thank you for letting me on. Ill contribute when I can but admit it will be mighty little as Im no mechanic. So here goes.
I drive a 2004 Ford 6.0 automatic f250 4wd with 99,000 miles and drive it lots of short (5 mile) distances. Truck is stock except for a shift kit. The last few days I have noticed when I start the truck it takes longer to start, not a long time by any means but it doesnt instantly roar to life but takes a couple seconds of cranking and I could tell a difference in the sound like the batteries were weaker. I bought two new batteries from les schwabs last summer so that shouldnt be the problem but who knows. This morning I get in my truck to start it and it sounds like it wont start. Sounded like super low battery voltage. It started on the second crank but the cranks lasted for a good 5 seconds. Once it started it purred but it did not want to start. I drove it a few miles and while driving the ABS light came on so I went a couple more miles then turned the truck off. It would not restart. It wouldnt even crank this time but made the sounds they make when the battery is too low to do anything but turn the lights on. I cleaned the battery terminals but they werent hardly dirty anyway and it didnt make any difference. I dont know if it would be something as simple as the alternator? The gauge lights and radio and such didnt seem to dim but the heater fan didnt seem like it was blowing as hard. Sorry for the long post, just want to make sure all info is on there. Id love to hear any ideas ya'all may have. I will take it to Les Schwabs later today to test the batteries if I can jump start it, figure Id give it a shot anyway. Thank you!

 

Very well could just be the alternator, you can jump start it from a car just let it charge a while, test the battery volts now and after it is running, it should be around 14 volts while running and if it is below 13.4 I would say alternator is shot.

 

Had this same problem yesterday. Started slow and 2 miles down the road gauges shut down radio cut off. Checked alternator and only putting out 11 volts. Replaced alternator this morning with motor craft from oriellys for 136.00 now putting out 14 volts all good.

 

Tjug glad that worked out for you. I replaced the alternator a bit ago then jump started the truck and it fired right up. Thought I was made in the shade but tested the voltage at battery terminals and it steadily dropped from 12.6 to 8.4 within a minute. I turned it off and went to turn it back on (not that it would) and the gauge lights would hardly turn on. 5 minutes later the gauge lights at least come on bright but no juice to crank it. Now that I know its not the alternator Im not sure... time to make some phone calls.

 

Make sure you got a good alternator and check all your connections! Can you start truck and test alternator output at post on alternator to verify? I have seen many faulty replacement alternators at shops lately. . . I also have seen a lot of bad " new" sensors too . . . Just verify repair before u go crazy. . .

 

I had OReillys check the old alternator I took in later and they said it was shot. I have not had the new one tested but plan to on Monday morning. Connections are good. Tested voltage on new alternator as truck was running and it was same as at battery testing from battery to alternator. Volts were in the 12 volt range to begin but after a couple minutes steadily decreased to 9 before I shut it off. After talking to my bro and bro in law and the guy at O Reillys they tell me if the alternator was bad (which it was) and if it had been bad for long enough it could draw the batteries down to a point where it could possibly ruin one or both of them. So at this point I am wondering if I now have bad battery(s) as a result of the bad alternator? Ill let the batteries charge overnight on the battery charger then see what they will do. Does that sound like a valid possibility to you guys with the batteries now being the problem?

 

I would charge them overnight and then have them load tested at local parts house. If one is bad its best to replace both. $$$$ let us know how it goes. These trucks are great when they run and a pita when they don't.

 

Well I let'er charger overnight. Batteries were showing 12.9 volts this morning. Started it up and drove it 4 miles to my shop. Stopped a couple times along the way to check batteries and they were at 14 volts. Drove home and checked it, still at 14 volts. Turned off truck and it dropped to 12.6 volts and stayed there so Im hoping im ok. The battery light stayed on though but voltage was good so Ill have them tested tomorrow. Thanks for the input guys.

 

When you first start the truck the batteries won't start to charge for about the first 2 minutes/so I have read/ so if you were testing it the first time within those 2 minutes that could have explained why the voltage was dropping, hope it's all good now.

 

Figured Id let ya'll know how it all went down. After charging the batteries overnight the truck has worked great since. Batteries tested good at les schwabs. The battery light was still coming on intermittently throughout Sunday and throughtout the morning this morning, but at noon it went away and hasnt been on since. I guess after the old alternator quit working it wore the batteries too far down and they just needed a good deep charge.