Prius died after I parked. Intermittent power. Able to start after 3 hours.

First of all you're treating the car like a Chevrolet truck It doesn't have a starter there's no key there's no cranking to turn the car on You push a button It's quite a bit different All the dimming lights and business going on is a definite clue as others will chime in shortly You want to find out why lights are going dim Do you have bad connections is the 12 volt years old in the 12 volt space where that battery goes Is it full of water take a look with your eyes If so there's a place to start usually most things involving Prius acting not correctly involve power as an electrical power like the 12 volt switches and buttons and computers do not like inconsistent voltage they will dim click rattle all of that sort of thing so you might want to check there All these behaviors are you're observing are actually quite normal for failing or not proper voltage getting to systems so you may want to start with the very basics like the 12 volt battery and that sort of thing once that situated lights generally don't go dim and things like that until the thing has been sitting there on unattended and not running and the 12 volt starts to lose power that should take at least an hour just sitting there not starting not running nothing.

 

Start by checking 12 volt battery voltage. How old’s the battery?

 

Checked with the car completely off, with a volt meter. That’s not good.

 

It's likely the 12v battery is dieing....
if it's a Toyota battery, you should be able to see the battery date on it.
It's unlikely it's the original battery, seeing the car is 12 years old.

If you have a battery charger of 4.5 amps or less, attach it to the battery and let it charge
for at least 8 hours. Wait about 30 minutes and check the voltage. If it's still at the 11 volts,
it's dead. Purchace a new Toyota battery, then charge for 8 hours, before installing it.

No store or dealership will charge the batteries, they just sell them.

 

You really need 12 volts on a 12 volt battery 11.8 on down or under 12. Is not a good sign of any of it now when you boot the car up and the charging circuit starts and you measure like 13.6 to 14.5 you know it's getting voltage from the inverter but I guess it can't keep that charge because after you turn it off for a while it goes down to this 11 business and that's below 12 volts that makes it not good.

 

OP post #7 with attached battery picture shows a label upper left corner with the manufacturer date 12/18. This little 12V battery, even though AGM, usually only lasts 4-6 years. If you have a charger conditioner, like this one, you may extend that to as much as 6-8 years. Also in post #7, your owner's manual has information on how to open the back hatch when the 12V is dead. There is a little square pop-off cover on the inside bottom center of the hatch door. Remove that and there is a looped cable that you pull to release the lock. Much easier than maneuvering over the back seat with that heavy little battery.

 

Had you taken it to Toyota, you would have gotten a discount because it is
still under warranty.
If you had used a 12v battery attached to the connector in the fuse box under the hood,
you would have been able to unlock the car and open the trunk....

Autozone doesn't know how to check the battery for the Prius.
Did you charge the battery? That would be a very good thing to do.
The inverter charges very slowly and you'll have to drive the car for 2-3 hours straight for
it to be fully charged. Driving for 20-30 minutes is barely enough to keep it charged.

I'm glad you got it going and it was simple.

 

I don't see why that would be.