2002 with red triangle and no codes

Yes when the car is on and ready at the 12 volt battery with a 12 volt or DVOM tester you should see 13.5 to 14.5 volts on the battery terminals with the car green light spelling ready The minute you turn that ready light off the battery will drop back to whatever it's going to sit at within 30 minutes so after you shut the car off in 30 minutes goes by and you come by and test the battery and it says 11.8 volts that's not good It needs to be 12 volts when standing If it's a real AGM and a very good battery it'll show about 12 5 12.7 standing when it's new. You might try a more capable scanner It sounds like your scanner is able to read basic p codes but may not be able to talk to all of the computers the 20 of them or so they're in the vehicle so there's always that If money is an issue something called an AP200 scanner gets pretty decent marks for a lot of this community's vehicles maybe something to look into sounds like you may have the hybrid battery isolation fault which usually a cheap scanner can clear the codes twice and make that go away until they turn the car off again. Then they have to repeat the code clearing process two times to get the car to run again It's quite annoying.

 

Ditto on checking codes with a different scanner and making sure your 12v battery is good. Do either of the three symbols light up in the dash display? If you have an HV battery issues, the battery symbol would typically display.

 

First order of business is, as other posters have suggested, make sure you have a heathy 12v battery.
And that the 12v charging system is working properly (sounds like it is not).
Assuming that the 12v system is sufficiently healthy and you still get these symptoms.....
I have seen this happen with P3009 (HV Leak Detected) codes from the traction battery.
Orange Triangle of Death, but no codes present to the standard OBDII reader.
The full cure is to either
(a) replace the HV battery pack ($$$) or
(b) tear it down and clean ALL the contacts, including those on the voltage sense pins going into the battery control ECU (those are the should-be gold pins in the orange connector).
Option (b) should only be attempted if you are confident of your HV electrical troubleshooting skills, take safety precautions, and are prepared to undertake Option (a) if you find there's too much corrosion in the battery pack. Or something breaks.

 

Sounds like the high voltage isolation fault is what you're describing there is a code for that I think but still sometimes it doesn't get set in the car starts acting weird there's a down and dirty test for this with a DC multimeter from the one of the studs of the plug on the HV battery to the frame should count down to zero if it stops like 80 or 90 volts or whatever that's your HV leak