Olds Alero Electrical? Alternator? Battery?

[Pete112288]

So my step-son has a 1999 Olds. Alero. He said that yesterday while he was driving ALL of his lights on his dash lit up. Like when you first turn the key in the ignition. I have seen this when a car dies but it stayed running. He said he also noticed at that time his speedometer was not working. A quick google search says things anywhere from loose wiring to bad battery to bad alternator. Any thoughts on this?
My wife also mentioned that she thought it has sounded lately like his car is not wanting to start as easily.
Frankly, I hope its a battery or alternator. I would rather replace one of those then go chasing wiring through the car looking for shorts or loose wires.
Oh, and he got a low coolant light not long ago, we topped it off and it went away. Then after the fact he said that if he runs his heater, mainly the defrost, and the car hasnt warmed up first, it smells like antifreeze. I am guessing that means bad heater core...?

[Woodchuck]

My SWAG is yes alternator and heater core. You can use a multi meter to check voltage at the battery while running, should be at least 13.5v. A heater core in that car is a large undertaking to say the least. Stop leak is not your friend. 

[Pete112288]

Thanks. I heard the first couple years of that car were easier to do the heater core, then it turned way worse in the years like after 2002 or 2003. However, that could be wrong though since that's just what I found on the almighty Google haha

[Woodchuck]

Replace
Heater Core   B   5.1   6.0
Does Not Include: Refrigerant Recovery Or Evacuate & Recharge AC System.
With a/c service, 7.2 hours. Parts won't be much but the whole job is gonna make a mess out of a thousand dollar bill.

[Zardoz]

 

Alternator, because I had a similar problem and that what it turned out to be.

Heater core maybe,  but you should be able to see water stain somewhere.

[Pete112288]

Well, pulled the alternator and had it bench tested. Out of 3 tests it came back fine each time. The belt is good. So I am gonna have the battery checked next.
Got behind the wheel myself a bit today and the battery light stays on all the time. None of the gauges on the dash are working at all. The lights on the dash work but none of the gauges. Sometimes after it is started then put into drive all the lights on the dash come one, everything, warning lights and all. They stay on for a second then all go off.