Jumping car every day

Who are you working with, and what was the replacement 12 volt battery? What happened between September and December, can you provide more detail?

What was the replacement hybrid battery, a new Toyota battery, or a refurb from independent?

You're correct the Prius doesn't have a traditional starter; it uses the power of the hybrid battery and the electric motors to start the engine.

Your last sentence raises a lot of questions: what was replaced in March? Do you have any invoices you could scan/photograph and post? Be sure to blank-out personal info, say with 3M stickies.

 

Has the charging voltage EVER been tested while the car is running ?

One of three things is happening:
The battery is not charging.
Something is not shutting OFF and is draining the battery.
The battery is actually bad.

Depending on where you are making the connection for the jump, there might be a loose or corroded connection on one of the main battery cables too.

 

If you're not throwing codes, then I suspect that your traction (big) battery is OK.

Methinks you have a problem with something like a dome light or something that's been wired into your car that's drawing down the aux (little) battery,
The aux battery does not "start" the car but it does boot it up.....and a non-booted car will not start.
Check that first....and by *check* I mean have it checked by a different entity than the one who keeps shoving new (??) aux batteries into the car just to get you out the door.

Speaking of which....
"Had this same issue and in March had the Synergy drive system replaced..."

One thing that MUST be replaced IMMEDIATELY is your mechanic!
Hybrid Synergy Drive - Wikipedia

A *new* battery does not always mean a *good* battery....but Priuses do not normally chew through several a year without a little help from the owner.
Your car is a 2005, according to your description.
If so, then it's in those awkward teenage years.
Look for aftermarket SWAG that might have been (mis)wired into your car's electrical system like alarm systems, remote start, or some goofy kid lighting or stereo system.....and get back with us.
As Sam excellently pointed out above, you might also have a wiring problem with the aux battery.

Good Luck!

 

how many miles on her?

 

Where are you in Ga? I'm in McDonough right now but will be leaving to go back to Columbia tomorrow afternoon. If you're close, I'd be happy to help you troubleshoot. I have my tools/laptop/techstream with me

 

There's a clue here. But I haven't figured out what it is.

 

NO it is not a blown fuse. Jumping in a good battery doesn't fix that.
It could be a loose or corroded connection right there at the battery posts.
But most likely it is just a very dead battery.
One thing at a time.

 

It might be a clue that a really lot of people have no clue as to how electricity works.......maybe ??

 

Checking the wiring from the Aux battery is super simple if you know how to use a $10 multi-meter and you know where the wires go.

After you boot the car up, are there no other symptoms? No lights? No abnormal conditions?

What about non factory accessories?
Any of those?

Has the car ever been in an accident? Especially a rear-end accident??
*are you SURE?*

If the only problem that you have is a dead aux battery......followed by another dead aux battery.....and another one after that (IIRC) I'm going to guess when you take your Aux battery out and deliver it to AutoZone it's going to be................(wait for it!)..............dead.

Something is causing this that's either super easy to find....or there might be a eeensy-weensie nick on a wire somewhere.
First thing I would do is verify that the battery leads are OK.
Probably the second thing would be to patch in a known good battery and power cycle the car and then measure how much current is flowing out of the battery when the car is stopped and locked and after it goes through all of the tossing and turning that Priuses do as they're going to sleep. (10-15 mins)
If you have a current draw on the aux battery, then all you have to do is find it....

Easy, right?

 

None of the above suggestions would explain why the car turns on without pressing the brake pedal and the start button. Whatever is causing that is most likely what's draining the battery.

Edit to add: I suspect mice in the wiring.

 

All those "battery testers" at places like Autozone mean nothing to a Prius. A standard car draws power off the 12v battery to turn a little electric motor called a "starter".

To start an engine you have to get it rotating first. It needs to be going and then you inject fuel and make a spark. If you've never done this:



You may not appreciate how much energy is required to move an engine. The starter in a car does what that man is doing to that vehicle that doesn't have a starter. When you hear a normal car start the chugga-chugga-chugga sound before the engine kicks on, is the starter. It is a lot of work for a battery and THAT is what the battery testers test for. Can I drain you quickly for a relatively long period of time, or not. A Prius does no such thing.

The 12v battery is not a "starter battery" it is an "auxiliary battery". It flips some relays which could be done with some AA batteries out of your TV remote control. It also primes the brake pump which is the whirring sound you hear when you first get in before you press anything which does draw considerable (30A+) from the battery, but for a starter that can draw 100A, 200A, 300A or more it is peanuts. Those relays the Prius kicks on enables the hybrid battery. Once the huge hybrid battery is online the car uses the hybrid battery and MG1, an electric motor attached to the engine, to start spinning the engine. After a couple seconds it injects fuel and spark and the engine is online. The 12v battery has absolutely nothing to do with it at this point.

So again, Autozone and other testers mean nothing to a 12v battery other than the voltage check which you can do with a $10 DMM as suggested above.

I would use the DMM and test check the 12v voltage when the car is off and has sat as well as when READY. If the inverter is damaged and not outputting the 14v charge voltage your 12v will never charge up.

Or it could all just be a gross misunderstanding of the car. The 12v battery in a Prius since it is used so lightly also charges lightly. If you drain the battery to the point that you need a jump to get it going, the Prius will need 8-10 HOURS of being ready to charge it back up. Most people don't drive 8-10 hours a day. If you jump it and keep the car on for 10 minutes it will never actually charge.

 

Sigh....we could have had this hammered out already, but unfortunately it seems our schedules didn't match up very well for you and I'm back in Columbia again...............if you are close to the Georgia/South Carolina border (Augusta area) I may be going there this weekend.

 

I understood it as: as soon as jumper cables are connected it can be started. If it actually starts by itself when jumper cables are connected it’s a big hint.

So does it start by itself when jumper cables are connected?

 

I did not read his statement that way at all.
Sounds to me like "things" just come alive when power is applied......like lights on the dash.