Recent replaced 12v battery dead again, root cause?

Assuming the SOC figures are coming from your tester and not the car (which does not have a 12v soc monitor) AND your 12v battery dropped from a high soc to low overnight, then its either a bad battery or an excessive off state (parasitic) discharge. Your low charge state could be either. Bad internal connections can cause failures on newer 12v batteries. Excessive parasitic draws can be caused by rear hatches not being completely closed or many other things. Typically measuring parasitic draw with an ammeter in series with the negative battery lead is definitive. A parasitic draw of 20 ma - 30 ma is normal within an hour after various computer functions turn off.

Most people would either take the car to the retailer that sold them the battery and allow the retailer to determine if a warranty battery is needed or they would place the battery on a good four stage charger for ten hours (if required) and then monitor the battery voltage overnight as an indirect indicator of parasitic draw.

 

charge it up and track it every night and morning

 

I’d second this. Here’s a how to:

 

These are the results from a recent parasitic draw test on my 2012 v:

1. Measured 21 ma steady state current. Varied from 20.3 ma - 25 ma. It was 20.3 about 95% of the time.

2. Opening the hatch or a door would draw 1750 ma which then dropped to 21 ma within 75 seconds after closing the door.

I did not break the 12v current path to insert the ammeter, so no major sleep delays occurred. I used a $400 meter and then a free Harbor Freight meter. The results were identical.

 

Did you do the series connection?

I did. Never knew about parallel. If you know, what would be the reasons to do parallel, and are there drawbacks?

 

The idea behind the pictures in post #5 is to be able to disconnect the battery and insert the ammeter without breaking the circuit. That keeps things from being reset.

step 1: connect jumper from post to clamp. current is flowing through jumper and cable.
step 2: remove clamp from post. Current is now going through the jumper.
step 3: connect meter from post to clamp. The meter is now in parallel with the jumper.
step 4:remove jumper. The ammeter is now completing the circuit.

Reverse it when measurements are finished to complete the process.

 

If your talking about the above drawings, it is series. The left setup allows you to maintain the circuit while disconnecting the battery terminal. Then you remove the jumper as shown in the right pic. On a Prius its easier to maintain the circuit by disconnecting the negative cable at the chassis with a jumper in place from the negative terminal to another chassis point. You avoid the computer shutdown delays.

Its easier than it sounds and you can use long meter leads to have the meter outside of the closed hatch.

 

I ran wires out across the hatch threshold, then gently closed the hatch on them. Plenty of give in the weather strip.

 

If you want to measure the current draw in the morning just run a pair of jumpers wired in series on the negative side outside of the hatch. Leave them connected to each other overnight. In the morning, clip on the ammeter to both leads before disconnecting their outside connection.

The root cause of the previous battery was likely a manufacturing defect that caused a high resistance internal connection. Sometimes a new battery works fine until they are jarred under high current draw. It can have sixty or seventy amps flowing under some charge scenarios, especially if the car was not driven for weeks or a light was left on for 12 hours or more.

However I think you are chasing ghosts at this point. Your battery was bad, now you have a good one and your parasitic draw is low. You can get an indirect indication by going into your mfd screen in the morning before you go to full Ready. DC voltage with no meter. A readout of 12.3v or above would be fine. With a new battery it may be as high as 12.6v. When you go to Ready, the voltage will rise immediately as the inverter takes over the 12v load and begins a charge algorithm on your 12v battery.

Realtime 12v Battery Voltage in Off or Running State
Check out your battery status/charging system by using the MFD Service Menu.

1. Press the Start button without the brake pedal

2. Press and hold the "CAR" button on the MFD while turning the headlights on and off 4 times

3. Press "Function Check / Setting" on the screen
-Function Check / Setting menu will appear

4. Press "Vehicle Signal"
-Vehicle Signal Check Mode" screen will appear, showing:

Battery 12.3v ---------SPEED 0 Km/h
IG OFF ---------------TAIL OFF
PKB ON ---------------ADIM/TCAN BRIGHT
REV OFF

The 12v battery voltage is displayed and changes as the load changes. Go to Ready and the 12v will rise at least to 13.4v (float charge) to 14.9v (high charge).