That 12V Battery...

The only purpose of the 12v battery is the start the electronics in the car and possibly lock and unlock your doors. It won't affect all the other things you've mentioned. This is a case of a placebo effect that will soon wear off

 

Come back here in a few days after the Placebo effect wears off and we can discuss a little more. There are many factors other than the 12v that may have contributed to what you're seeing.

12v battery doesn't really do much in a Prius, that's why it's this little tiny small battery. In fact you can disconnect the 12v battery after your car has started and you shouldn't notice any change in your car's performance. Many people here put a big emphasis on the 12v's magical powers, it really doesn't do that much.

 

Thank you for the report.
That same experience......and advice......is present on here in probably a hundred different threads.
Now 101 !!
P.S. Bad connections can cause similar problems.

Also.....if you are watching a long term gas mileage number, that really is pretty useless......because it changes very slowly and takes into account things that happened years ago.
I reset mine every time a get gas.......or watch the one that resets automatically for every trip.

 

Some maybe but mostly NOT.
What if the weak battery causes the "electronics" not to start properly ??

You have been involved in discussions like this on here long enough that you SHOULD know that your statements above are incomplete, misleading and often just plain wrong.

 

If the car starts and goes ready, what electronic didn't or could have not started?

 

An actual failing 12v that tested bad should be replaced but I don't want readers to be mislead by all the possible benefits by just replacing your 12v battery.

These batteries are $200+ in some cases and in "last ditch efforts", people will read these posts and say "what the hell, "since I am experiencing issues, I'll just throw in a new 12v to see if it'll fix my issues". This is done over and over again because of posts stating the magical powers of the 12v battery. It is NOT A MAGICAL DEVICE. It starts the car's electronics......that's about it. After the car is in READY mode, the HV battery runs the show. It will not fix a weak hv battery, it will not increase your MPG (unless the 12v is actually bad and has a failed cell), it will not make your SKS suddenly work if it didn't work before, none of that.

 

when the sks on my 2004 stopped unlocking the drivers door while in my pocket, the buttons still worked and the car started and ran fine.
a new 12v fixed that one problem

 

What we have here is a failure to communicate.

I did NOT say that anything did not "start".
I tried to say that low input voltage may cause it to start incorrectly......with internal errors or cause it to report false errors.

 

It is not misleading to state the possible benefits of replacing an OLD or worn out battery.

It is even absolutely true that sometimes the first "test" will even show one good when it really isn't.

What is irresponsible is to lead people into spending time and money changing out parts costing MANY times as much when the battery really IS the problem.

I don't remember ANYBODY on here EVER suggesting that there is any magic involved.

I think you either need to read more carefully or work on your reading comprehension.

 

GASP.
Some things DO rely on the 12 V battery before the car "starts".
Imagine that.

 

there is also a very old well known thread here regarding strange electronic glitches and checking the 12v

 

i would check the voltage

 

Well, my neighbor JC91006 may be onto something.

Unless you've done something like listen to the radio for an hour while waiting outside of Church like my dad did, basically something obvious to kill the battery, these AGMs are pretty robust.

New battery dying again is my suspicion, but cause may be the alternator, or dc-dc converter, whatever charges/provides 12 V power...

moto g(7) power ?

 

AGM’s might be robust but a Prius battery is as big as a kiddie car battery. Don’t confuse an AGM that turns a starter with the clown car Prius battery.

 

You’ve disconnected the battery, resetting the computers? Or did you keep the electronics powered, while replacing the battery? I got lazy when I replaced the battery on my parents’ v, so I connected a battery charger to the jump points under the hood while I swapped their weakened 12V with the Chinese LiFePO4, the reason I asked. So I did not have to do all the reinitialization because my parents car has the fancy parking aid, the one you can release the steering wheel while it helps back you into a spot.

Placebo effect could be the computers starting with blank sheet of data, starting to reinterpret an unhealthy HV battery.

How did you verify/determine the 12 V was bad? My parents kept reading just under the healthy voltage, in the range that the service info says to recharge and retest. But it was only 0.0x V low, I think 0.04 V to be precise. It kept reading 12.46 V, and healthy is 12.5 V and up if I recall correctly....

 

True, but small battery also means easier to charge. We are talking about a battery limited to 4.2 A maximum charge rate. Even with 6A charge rate it would seem to overload the battery. Charger would charge to full, but if I quickly disconnect and reconnect charger would start charging again. (Battery would not truly fill). How much MPG are we talking about losing with 4.2 A 14 V of power, 58.8 W of juice being sapped by a bad 12 V?