Power Outage

Did I get this right? Voltage at 12V battery posts is 2.4V when it’s connected?

Of course Prius can’t start when 12V battery is that low. So charge or replace the 12V battery.

 

the 12 volt powers the computers that start the car if its low or dead car no go...
a volt meter does not test under load so that 12.8 is almost meaningless.. its resting voltage.
replace it , you cant do anything before the computers power up

 

how many miles on her?

 

Are you confident the key is working properly? Not starting with a jump is very strange.

 

Did you use the jump connection under the hood? If so, make sure the side of the jumper clamp that is actually contacting the metal side of the terminal on the car has 12V on it. Some cables have 12V on only one side of the clamp and if that gets connected to the plastic side of the terminal on the car, you have no juice.

 

If the voltage measured at battery terminals is 2.4V then either battery is empty, faulty, or your measurement is wrong.
What was the voltage when you tried jump starting it?

 

if the battery is only a few months old return it and get a free replacement ...

be sure you clean the negative cable connector where it attaches to the cars body.. if that doesn't fix it the next common sense thing is
you have a dead short to ground that could set the car on fire so Id start pulling the interior and carpet out and look for burn marks where the wire harness is touching the body.. not sure why it isn't blowing fuses.. did you check the one near the positive terminal on the 12 volt?
the orange safety plug on the HV battery is also a fuse, might as well check that..
my money is still on a bad battery

 

Connect your jump pack to jump terminal under the hood! I don’t understand what kind of jump pack would be impossible to connect to jump terminal.

Measure the voltage when it’s connected. When it’s connected to jump start terminal if there is still no voltage at jump start terminal then you have bad meter, bad jump box, or bad connection on the jumper cables. If there is voltage at jump start terminal but not at 12V battery terminals you have burned fuse/fusible link, or bad connection on 12V battery cables.

 

Navy commander is right about the jaw connection on the jumper but the jump point under the hood provides a metal tab
The jumper can clip too on both sides of the clamp. That clamp one side thing got me once too lol.

Beach bum is right too......if you had a dead short on the battery lead very exciting things would happen.

So you have a dead battery. Don't jump it don't charge it replace it.

 

OK I throw one last idea then I give up...
next to the 12 volt battery is a black box, disconnect the white wire connector and leave it out, disconnect the 12 volt battery from the car, remove it and look for swelling or leakage.. if it looks good recharge it, reinstall it, reconnect the white connector be sure it clicks and pray.. a 2004 isn't worth a trip to the dealer.
still, get a new battery

 

If it's under warranty why are you reconditioning it? A Prius AGM that's perfectly discharged by a light left on
Usually is never the same. It's a very small battery. If there's even the slightest possibility it will expose you to another jump start down the road replace it.

You will really regret it if you don't.

 

Yeah that's what that little battery does. It usually does not recover.
The hatch light gets lots of people they leave the hatch not closed all the way and the light is on and it kills the battery.
It's on the drivers side in the back hatch it has an on/off switch turn it off,

People that kill there Prius battery all have one thing in common, they do not arm the alarm especially in the garage. Door ajar will not allow u to arm the alarm alerting you to the fact the door is ajar and the cabin light is on. Caught me numerous times.