A battery while not being connected to a working charger ( or alternator ) will show its highest voltage when it is not feeding a load. The battery can only provide the rated CCA when fully charged. When feeding a load the voltage will drop, depending on the amp load and the amount of charge in the battery. If a voltmeter across the battery posts shows around 14 Volt with all accessories ON and engine at a fast idle, then the alternator is working properly. As Gorn mentioned, make sure there is nothing drawing current when it should not. Silly things like a light staying ON in the glove box can drive you nuts. On computer controlled cars there is always a small amount of current being drawn, less than 1/3 AMP which is used to retain settings on electronic equipment; however, the battery should be able to hold this draw for weeks without going flat.

 

It does the same thing with another battery so it's not the battery.

 

There is a Theft Deterrent relay controlled by PassKey in line with the solenoid purple wire.
If PassKey is satisfied with the key, the module will energize the relay thereby allowing the starter to work as normal.
You could pull the relay and replace it, or, jumper across the two purple wires in the socket just to see if starter does crank.

Over time with usage, relay contacts, as they close and open, generate a minute spark and this spark deposits a little carbon onto the contacts, and builds up resistance for the current going through the contacts, 100% power in, maybe 50% power out, the remaining 50% goes up in heat.

 

From her other thread:
By default, the theft deterrent disables the starter and the fuel injectors. Her starter was working at first. If the theft deterrent malfunctions, is it able to pick and choose which one it disables? Or perhaps she now has more than one thing causing this.

 

I can try to record this noise if I knew what to use and how to get it on here. When my husband gets home, he's going to see if it jumps. Not sure what that will indicate based on the results. I can put it in the shop after Christmas if I have to. I prefer not towing it. I HAVE to have it running by Jan 13th. It will be the only choice I have to pick my kids up from school 2 days a week. Just a pisser that I FINALLY had it on a reliable basis for 5.5 months and here I am back to day 1.

 

I don't think it makes a decision, just does both in parallel.

Magic words, starter was working, but nothing now. Could be anything, just need to eliminate the simplest first.

 

Just in case anyone isn't following the "battery" post, we swapped batteries and tried jumping the battery in it. Same result, didn't make any difference. The belt rotates a little and that's it.