Low Votlage on 12v Battery even with new battery.

You have a parasitic drain somewhere

 

prius doesn't bring up a low battery very well. put a charger on it. should be close to 13v. then monitor it every morning to see how far it drops. if it keeps dropping, something is draining it, or it is not being charged properly. you can measure that with the car 'ready'.

^tanks mention of a parasitic drain simply means that some fault in the car is draining the battery when it's off, more than toyota designed for.
but you need to know if you have a good, fully charged battery first.

 

Nothing funny about it. What an odd comment to make.

That is one possible cause for the extremely low voltages you are seeing.

It is also possible that your new battery was not charged when you got it.......and the car itself is not capable of fully recovering a DEAD battery over a short time like 3 days.

It is also possible that your charging system has failed. What is the voltage reading while the car is running (in "ready" mode) ?

 

"No, If I have my prius on Ready Mode, Aux 12v battery read at 14.1-14.4v and same as my Original Toyota battery 14.1v when Ready Mode is on. "

That is the charging voltage of the Prius system; nothing to do with the health of your battery.

"i don't have external AGM Charger. Don't know if can charge from my None AGM 12v battery?"

You can't. You need a battery maintainer that charges your Prius aux 12V at 4 amps (or less; less takes longer...). A maintainer will taper off its charge as it approaches full charge; won't overcharge the battery.

 

The voltage when READY doesn't tell you the condition of the battery, just the condition of the DC/DC converter in the car. The good news is, given you're seeing the 14.1 to 14.4, the DC/DC converter would appear to be ok.

 

if you don't want to buy a volt meter, search for the instructions on how to read the voltage on the screen with car in acc mode.
or you could go to an autoparts store for a free load test.

what brand is it, and where did you buy it?

 

yes, there's a small draw, so the battery is a little better than that

 

When the vehicle is running (in ready mode) you are NOT reading the actual battery voltage but the voltage of the charging system in the car.
To read the actual battery, the car must have been OFF for a while.

And to be sure that "phantom loads" aren't affecting THAT reading, one of the battery cables might need to be disconnected.

AGM batteries are not THAT different. Any "good" charger will work fine.
That does not include cheap trickle chargers......which are not fine for anything.

 

Can't what ??
A normal, manual battery charger will be just fine......IF the capacity isn't WAY high and you disconnect it when the charging current nears zero.

 

11.8 V indicates that it only has about a 40% charge......and may not operate things properly.

 

If "from My Prius Screen" in the above meant "from the Vehicle Signal Check screen on the MFD", that should be taken into account.

As has been often covered here on PriusChat, including in a recent-enough thread to be fresh in memory, that vehicle signal check screen reads a voltage from the inside of the MFD where it is often half a volt or more lower than you would see at the battery. On any Prius I've owned, if the signal-check screen were showing 11.8 to 12, a battery measurement would be around 12.4 to 12.7.

 

The onboard charging system may NOT be able to fully charge the battery if it really IS very low.

It would be a MUCH better plan to connect the charger that you have for a few hours........IF it has a meter to monitor the charging current.
And why did you think mentioning the temperature would add any useful information to the discussion ??

 

post the code from the top of the battery, it has been covered before.

at 12.27, you want to keep a close eye on it. depending on age, things can change quickly