98 F150 4.6L 4x4 Ext cabCranking was a bit more sluggish this past week, harder to start on cold mornings, then it wouldn’t start after a couple of short drives and restarts. It starts with a jumpstart.It was a new Napa battery a month ago.

Found the positive terminal partially broken so replaced.Alternator charging previously appeared normal, no load check but was pushing ~14.4 volts, which I thought was normal. But since the no-start, alternator is pushing 14.8 v on start, dropping down to 14.6 after running a while. Is that overcharging?

Battery shows 12.6-12.8 after charging, but doesn't appear to have much power.

 

Make sure the cable connections are clean and making good contact at both ends, at the starter too. Get the battery load tested.

 

Even though the battery is new, doesn't mean it's any good. A lot of times those batteries sit on the shelf for a LONG time.

I prefer to get batteries direct from a battery supplier.

 

Go to a parts store and get both the alternator and battery load tested. They can do it in the parking lot without removing anything.

 

Your meter may not be accurate.
Normal system runs at about 14.1 v.
The rise in voltage has to occur in order to force current into the battery to recover it.
As the battery recovers, the voltage recover at the battery lowers.
The control for this is the regulator that controls the alternator field winding.
The reference for this voltage is in the regulator.
Seems either the cables, posts, terminals have an issue or the battery has an issue under high load.
Voltage only without a load is not the whole story.

 

Turned out to be the starter.

Changed partially broken positive terminal connector (only 1 of 2 bands around terminal). No start
Figured it was in starting system cause battery draw significantly dimmed lights on start attempts.
Solenoid - couldn't tell from resistance (S to ground) or voltage across when trying to start, but noticed motor cranked a bit when I jumped the main lead poles, so I replaced. Still No start
Removed the starter and bench tested to be working, partially then not, even without a load on it (i.e., flywheel), so I replaced, It started right up