Correct running volts?

[Schurkey]

So what is the minimum voltage the truck wants in order to crank? And what part is seeing this? The ecm I guess?

A fully-charged battery with no load, carries 12.6--12.7 volts, somewhat depending on the battery construction and battery temperature.

12.5 is 1/4 discharged. 12.0 is essentially dead.

During cranking in cold weather, you'd want 9.x minimum. Higher is better. The heavy amperage load from the starter motor will drop battery voltage significantly, as does cold temperature.

 

[454cid]

A fully-charged battery with no load, carries 12.6--12.7 volts, somewhat depending on the battery construction and battery temperature.

Why do I sometimes have batteries just off a charger that will show 12.8 or 13.x? I've had this happen with several of my batteries, but not all of them.

 

[Schurkey]

A freshly-charged battery has "surface charge". Often goes over 13 volts.

We used to put a 50-amp load on the battery for five or ten seconds. Probably SHOULD have waited for the battery to cool from charging. The surface charge will--eventually--go away on it's own.