What keeps killing my battery ?

Look for phantom loads?

 

Maybe......maybe not.
Some batteries just go bad; some the DAY after being installed.

Some testing needs to be done but you will need a multi-meter for all of it.

There are several pretty detailed threads on here already about chasing down "phantom drains" when the car is OFF.
Sometimes it is not a phantom drain at all and ends up being something like a door not closing all the way and leaving the dome light on.

 

You need a multimeter, a fuse puller, some information (watch the video Mendel linked) and some common sense. This is not something anyone on internet can solve for you. We can only offer "methods" of troubleshooting. If you've been wrenching on cars for ever, then you most likely have dealt with parasitic current draw before, but maybe not. In any case, best of luck and keep us informed. There are always useful lessons to be learned.

 

The first lesson prius drivers learn is never use acc to listen to the radio like any other car on the road, the 12v will drain in minutes, then will require a full charge to get back to normal.
The prius comes with a deep cell battery that can be drained and recharged several times, if you have a non deep cell battery (aftermarket) that's a problem.
If you have a parasitic drain like rodents chewing, you need to address that problem.

 

since it happens so infrequently, might you have left a light on or door ajar?

 

Well, when it comes to troubleshooting a battery then, guess I’m SOL.

 

Like all dressed up & ready to be hit on? I'm going to need to see photos of these... city parks.

 

Barking

Definitely barking up the wrong tree. Even if there was a Toyota tech here they would not be able to diagnose your problem over internet. You need hands on work. Strangers on internet can’t help in this case.

 

Gonna stop watching this thread.

 

Just a shade-tree wrencher, but here goes.

The most common causes for a dead battery in no particular order:

dome light left on

door left ajar (triggers dome or trunkspace light)

aftermarket OBD dongle that isn't smart enough to shut itself off when the car shuts down:

The onboard diagnostics port supplies constant power to any interface plugged into it. It is the responsibility of the user to make certain the interface "dongle" is either disconnected or shut off to prevent drain. Some people use these devices to connect smartphone apps like Torque or Dr. Prius to monitor their cars. Some people have dongles from the insurance company to monitor their driving habits for rate reductions. Some people have jealous spouses who install GPS trackers.​

smart key system:

This is a complicated one. The car normally uses very little electricity from the battery to listen for radio signals from the smart key. But if it thinks the key is near, it wakes up a bit more, using more power. Some owners have found that a key stored near or in the car is a recipe for a dead 12v battery. This is not limited to the Prius, several other brands are using similar smart keys now and they're getting the same disappointments the next morning.

I don't have a car with a smart key system, so I haven't had the opportunity to play with this firsthand. However, I have read about it in a number of threads on this board and other forums related to other cars with similar RF key systems.

The prius has a mechanism to let you temporarily disable the smart key system to eliminate the normal parasitic draw for long term parking and storage. Owners' manual has details on usage.

Good luck!​

 

You are making a lot of BAD assumptions here.

Without a VOM, neither you nor a "technician" is likely to ever find the problem in a timely manner.

An internal battery defect can make a battery go from 12.6 to (pick any number less than that) in any amount of time.

Typically, people who work in the service department are not well trained "technicians" and some don't even really understand electricity.

What we have here is another case of "Dont' confuse me with facts, just answer my question exactly as I asked it, because my mind is already made up."

Alas, it is likely that nobody can help you.......because you aren't listening.
P.S. I've been an Electronics Engineering Technician for about 50 years now.

 

Obviously...

 

If YOU can't recognize good advice when you see it..............

YOU don't know what you don't know. Sad.

 

OP:
First thing first:
I'll do you the favor of answering your question...

No.
I'm not aware of any Toyota techs that regularly post here.
At least I don't remember anyone who regularly posts here that admits to it.

No.
There is no "common" cause for G3 battery failure other than what we in the electronics field call a dead short between the seat and the steering wheel.

The Aux battery is a known issue with the G3, (too small, improper voltage management system, etc...) AND you have to remember that your car is nine years old now, has SOY BASED WIRE (it tastes like Doritos to mieces) and WE don't know what interesting alterations that have been made to the wiring, any accidents that have occurred with the vehicle or much of anything else, other than you're frustrated .

So:
Since you're not listening to any advice offered thus far, and since I've answered your questions...
I wish you fair winds and following seas!
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Advice for people searching for the reason why their aux (12v) batteries keep failing:

1.) Bad batteries are sometimes....bad batteries. Prius Aux batteries need to be NEW BRAND NAME batteries....not some cheap recycled unit like they sell at places like Battery Plus. Unlike the cars you grew up with, the 12v battery in a Prius doesn't "start the car."
It boots the car up. This is a VOLTAGE thing, not a current thing. If you do not know why this is important, then do not be discouraged!!
As we see above, sometimes KNOWING that you do NOT know something is a good thing.

2.) In a car with a proper voltage management system, you can leave the dome light on, walk away, come back an hour later and the dome light will be OFF. It does NOT work this way with a G3 Prius!
The headlamps will auto-shut off. (my headlamp switch stays on all the time) but if you leave your dome light on you will suck your aux battery dry.

3.) You need a real meter to really measure individual circuits to determine whether there is a parasitic current draw, or the batteries are dying from cockpit error.
Yes.
Sometimes the current leak can be intermittent, but a properly trained electronics technician will always verify FIRST what they can verify FAST.

THIS is one of the better videos I've seen to make sure that you do not have a consistent parasitic current draw.
NOTE: The G3 Prius has an ironically named "Smart Key"
Make sure that this is away from your car before you test the individual circuits since the proximity detector will 'wake the car up.'

Anyone interested in troubleshooting beyond this instead of just grousing, please mention any aftermarket equipment that's been wired to the car, wrecks, past rodent infestations, flash flooding, etc in your initial post.

Good Luck!!

 

Superb rundown on the answer, and GREAT video linked there. Thanks.