The Battery will not hold a charge, but diagnostics show the battery and alternator are ok. It won't even jump off at this point.

Is the alternator charging , with engine running connect a volt meter to battery should show around 14.2 volts , is there a short , remove leads from battery over night , if it starts in the morning there is a short circuit, if the battery is nun down it's faulty even though it's new .

The alternator should be showing at least 15 volts when running! Anything lower would indicate the alternator is at fault, since you say it is showing below 12 volts even for 2 minutes indicates a fault.

there still could be a fault with the battery not holding its charge or something draining the battery like a wire shorting or trunk light staying on that is making the battery go flat!

Could be a bad battery, and or alternator, if the alternator does not charge the battery when the vehicle is running your battery will drain causing no start.

voltage regulator. it may be in the alternator, or remote mounted. ((the alternator can be charging, but if voltage regulator is'nt working then it won't allow voltage to get back to the battery to keep it charged

Depends.
If the alternator is charging, and the battery will not hold a charge, I would suspect the battery.
If the alternator is not charging the battery, I would look at the fuseable links and connections.

Hi there !

I won't say its an alternator problem because the alternator only charges the battery when its on, And it should start with the jump cables even if the battery and the alternator are bad. your Issue is not clear. Does the car start when you jump it ?

Get the battery & the alternator checked (Autozone, O'reilly's or even Pep Boys can do that for free). If the alternator is out or going out, it's not charging your battery - that means everything electrical in your car is now trying to run directly off the battery & draining it (it doesn't take long - especially if the lights or A/C is on). If those check out ok, take it into a mechanic & have them run a diagnostic - you may have a relay out. Good Luck.

THE BATTERY LIGHT COMES ON TO ALERT YOU TO THE FACT THAT THE BATTERY IS NOT BEING CHARGED BY THE ALTERNATOR, IT DOESN'T MEAN THE BATTERY HAS A PROBLEM, HAVE THE ALTERNATOR TESTED FOR PROPER OPERATION.

I'm an electrical engineer and the two solutions posted are spot on.
If it jumps and runs ok then all fuses and wiring are ok.
Most likely your alternator is not charging the battery effectivly. A voltmeter applied while it is running will show the charging voltage (if any). So in effect you are running on battery power only until the battery final dies and is recharged. The battery dies when you try to start (heavy amp load) but still has enough energy to handle the running load (much less power than starting).

its the battery. the battery holds the charge and the alternator charges it so when you jump the car it stays running because you alternator is providing power when you shut the car off you have a bad battery that isnt holding the charge needed to start it again.