After the truck sits for a few days the batteries are too weak to crank.
No problem when I drive the truck more often.
The Motorcrafts that are in the truck, '06 6.0, are 3 yeras old.

 

I'd get the batteries as well as the alternator tested before just buying batteries.

 

Yup get them load tested and see what is going on before throwing parts and money at it.

 

I purchased two Costco Kirkland batteries a little over a year ago. These are Mfg by Johnson Controls who also builds Interstate, Motorcraft, etc so they are top quality.

I just had to have them replaced as I couldn't keep a charge on them. In doing an egr test at my service shop, I needed 11.7 volts and they wouldn't even allow for that test. Showing 11.5 volts. WTH?

I tested my factory alternator at the alt terminal and it tested at 14.2 volts so the 110 amp alternator is working. I just don't think it can handle keeping two group 27 batteries fully charged. Headed for a new 140 amp unit.

 

HI Millers...don't know about 2006'S but My 2003 allows the replacement of the 110 amp amp unit with the 135 amp alt which is the upper mounted alt on the dual alt trucks..direct bolt in.. I installed New Bosch.(about $165.from Amazon) lifetime warranty with no mileage restrictions...cheaper than a lot of rebuilts...good luck,Dave

 

^^^ Ditto ^^^

...unfortunately if one battery is weak or bad, then you should replace both. It's a pair thing.


biz

 

Try an equalization charge in parallel at around 20 amps. Monitor voltage and current. Probably take quite a while, since they are almost dead. The idea is all the cells in both batts have to be on the same sheet of music, because electrically it's simply one large battery.

Done periodically this would increase service life. This should also be done with new batteries prior to installation. Usually takes several hours to top off.

 

you could try a pulse charge it can bring back a battery life


I personally buy second's from interstate and have not had any problems

 

Does anyone ever upgrade there ground wiring to something that conducts better? If this is a common issue that may help take some stress from the batteries and alternator.

 

Sears platinum are Oddessey batteries rebranded, top of the line, imo. Also check out DC Power for alternators and upgraded power and ground cables. I went for the 275 amp (I think) on old truck. Made instant difference. Lights brighter, started easier, and idled better. Stock hot idle is like 60 amps, your headlights eat that much.

 

I worked at Sears and we had more problems with the platinum's. We stopped even trying upgrade people because half the time they would come back a few months later. We always tested the Alt before installing a battery, so we know that wasn't killing them.

 

I have owned my 1999 Super Duty 7.3 liter since new. Batteries do not last longer than 3 years. I have tried Interstate, Motorcraft and others. At 3 years almost to the month, no start. New batteries equals start. I usually get credit for the remaining "life" of the 60 or 72 month batteries I take in as core exchange. Replacement of the batteries at 36 months has become a fact of ownership.

 

Weird, zero problems on three sets I've had, post alternator upgrade. If it was a 7.3 or 6.0 just because the alternator tested good doesn't mean it was adequate to recharge battery during use. those diesels use an incredible amount of energy during start up and for about 10 minutes after during cold weather. If user starts up,drives five miles, shuts down the batteries didn't recover. Repeat daily and in a couple months you've killed them

 

These were cars and SUVs that would come in with problems. We rarely saw a diesel in the back. It might have been they were killing them driving so short distances or the batteries sat to long on the shelf. Who knows, I only worked there a couple of months before I got out of that place. If the batteries work for you them that's all the proof you need. I usually only get a couple of years out of a battery before I have to replace it anyways since I run extra lights and stuff.

 

X2 on getting the charging system checked out and X2 on replacing the batteries in pairs.. I did not on my 84 6.9 diesel and it ultimately cost me a starter as well because there was insufficient current to crank it over properly.
One battery had gone bad with a bad cell, which caused high current draw which evidently weakened the second battery. I replaced the first battery and the second battery only lasted a couple months, but in the process the starter crapped out.

-edit- I should add that this was back in 1987 so the truck was still pretty young and only had about 30k miles on it.