Has anyone had these odd electrical symptoms? 12V battery keeps shorting out each use

Do you have a volt meter? If so, use it to measure the voltage of the 12v battery.

 

After you jump it the 12v battery does not have to supply any current. The car is supplied 12v by the inverter converter taking high voltage and converting it to 12v.

Since a jump Readies the car, the connection from the jump to the electronics is fine.

The optimum test for excessive parasitic draw is an ammeter in series with the negative battery terminal.

However I would take it out and have it load tested at an auto parts store. 98% of the time cars with your symptoms turn out to be the 12v battery.

A voltmeter test is not good enough since a bad connection inside the battery can supply the micro amps need by the meter.

 

The way to diagnose something is to do some testing, not by assuming that something is good. You apparently do not want help with the problem since you dismissed the first thing that should be done in your situation. Good luck with your car.

 

You have a complete misunderstanding of how the Gen 2 Prius works. The 12v battery does not provide ANY "juice" to actually start the engine. The 12v battery merely supplies the power needed to start up the electronics, Once the electronics determines it's ok to do so, the main relays in the hybrid battery are closed and the hybrid battery is placed online. It's the hybrid battery that supplies power to the transaxle to spin the engine for starting (there is no 'starter motor').

Take it or leave it, the advice you were given is sound, because it sounds like your "box" is powering up the electronics, which is allowing them to do their job, and then once the hybrid battery is online, the inverter takes over, similar to an alternator on an ICE car.

 

How hard is it to connect a volt meter to the 12v battery and take a measurement?

Like they say, you can lead a horse to water, but you can not make it drink!

 

You passed the first test. Now, turn on the headlights and measure the battery.

 

Take apart, clean and inspect all the connections around the 12v and make sure you have a healthy fully charged 12v. This is a known problem with Gen2 Prius where loose connections back there leads to an abnormal shut down sequence. You know you solved it when shutdown sequence shows the gear shift indicator lights as the last thing to turn off on the speedometer screen (aka: combination meter).

 

There is more to the 12v system than just the battery. The (-) ground cable. The (+) cable connecting the battery and at the fusebox. The clamps, etc. It's not difficult to put a meter on the cable connection in the underhood fusebox and monitor the 12v voltage while trying to start the car. You just need to follow a structured, logical troubleshooting procedure. You KNOW everything works with a jump pack, so it's likely everything downstream of the jump pack connection is ok. It could be something as silly as the terminal clamps being too high up on the posts or just an internal battery failure. Where are you connecting the jump pack?

 

You do not need to start the car to turn on the headlights.

 

Correct, it's not a charge issue, but 12.6 volts is too low. Put your battery on a high amp smart charger.

 

yes, that's problem you can fix by looking at all the connections around the 12v.

 

Which is exactly how a battery with an internal failure or bad mechanical connection can act. When there is no current flow, full voltage can be read at any point where the battery is connected. As soon as any current flow tries to initiate, the open circuit/bad connection can cause a full drop of voltage across that connection, resulting in no voltage available for anything else. That's a bit simplified, but should be understandable.

Have you tried pressing the power button with your foot NOT on the brake?