I posted a thread earlier about a starting problem which I thought was the battery. Took it in and had it tested and it tested "good" and fully charged. It was okay for a few days and read 11.9 volts when I parked it, let it sit for 3 days and the voltage read 11.1 and it would not start. Put in a new Interstate Megatron, heavy duty. One curious thing was that the Motorcraft battery (BTX-59) that was in there is smaller than the Interstate. The Interstate fits the battery tray better than the Motocraft and the service station computer said it was the correct one and the Interstate site shows it to be the right one, MTP65. I looked at the Ford Motorcraft site and it shows the BTX-59 is for the 4.2L, so did they put the wrong battery in my truck??
My question: Why would it have tested "good" at the service station when obviously it was not? What do those testers read and has anyone else had a similar experience with battery testing?

 

perhaps they tested it wrong. I always try to get the highest amount of cca battery that will fit. Not sure how old your battery is but 5 years is the avg lifespan. The cold will also affect it.

 

If it was the original which is possible because it was a Motorcraft then it would be 7 years old so it was at the end of it's life cycle. This Interstate is the Mega Tron Plus and has more cca than the one that was in there, very heavy duty and I have always had good luck with Interstate. My Edge is showing 14.2 volts when running. Is that in the normal range for this alternator?
2005 STX SCAB 4.6L 4X4