AGM battery for Gen 4/Gen 5 Prius/Prius Prime and observations on the 12-V charging system

This is not the behavior I have witnessed in the year of owning my Gen5. The 12v charging does not care if you're in park or drive. It will operate the same and deliver 14.3v as it normally does and then cycle down to 13/12.7 temporarily during its routine cycling.

 

I second this! Ive been monitoring mine with the BM2 through an OpenMQTTGateway and Home Assistant... my goal now to have the car remote start if the overall levels of both 12V batteries gets too low

 

thanks, wait until you see the latest updates and the Gen 2 build!

 

if anything... I can say this is bad for the engines without the latest engine internal upgrades... like say a 2017... yep! I plan to test this theory on a newly rebuilt engine but thus far I'm willing to bet money that I can prove the engines without the latest internals are highly prone to head gasket issues just sitting in park and in READY.

 

No it doesn't do anything to the engine as it never comes on with the Prime, it stays in EV mode the whole time and powers from the traction battery.
Here is the log of this morning of my 2019 Prime. Last night the car was charged for 2 hours and the traction battery would have been in the high 90's % or could have been fully charged. The charger was unplugged from the car and the car sat overnight. 10C temperature this morning. I checked the 12V battery voltage with my BKmonitor and it was 12.6V when I started the car. I left it in Park and set the BKmonitor to log. Here is the log which I stopped when I left for work. Car displayed 96% for the Traction battery charge. Now I bought this car just about 3 months ago, so I do not know the state of the 12V battery but I do think it might be over it's best from past ownership.

 

So Gokhan, trying to understand what you are saying and what my Gen 4 Prime did this morning.
Would you say:
1.) it stayed on 14.3V because Daylight running lights (DRLs) were on?
2.) or it stayed on 14.3V because the current capacity of my 12V battery is low even tho it was at 12.6V at start up of the car?

I must say I suspect the state of the 12V battery. Maybe the DRLs drag the battery so low at start-up that the system then kicks into the 14V charge mode. Don't think I will go and rush out to buy a new one as I have had no issues yet and they are eye-watering expensive here, but I will keep an eye on it.

 

there's many sides to this tho... having the car in charge mode until the hv is fully charged while having the 12v battery connected to the 12v battery/system of a Gen 2 Prius for hours at a time for multiple days to months... the 2017 motor wasn't optimized like the later years engines were. To say I experienced the same initial smell of coolant and then the lack there of like I did in my Gen 3 which had significantly more miles on it, there is something to be said about the ICE constantly on and or constantly ICE on and off more than say the car did when it was fresh off the showroom floor. Once I figure out the engine testbench, the plan is to use a few non changed headgasket motors to power something large.. then when they go out.. install a brand new fully rebuilt engine and see how long it lasts under this load.

 

I fail to understand how all this has any relevance to what we are describing/discussing here?
On my 2019 Prius Prime (a plug-in hybrid) the ICE never kicks in when the traction battery has enough charge to power the car in City EV mode(which I use) at low speed or at a standstill. The ICE doesn't even start up when the car is started up. I've done 1600kms on 15l of fuel the last 1.5 months.

 

Currently with the cooler temps I’m seeing 14.4 volts continuously from READY, driving and PARK mode.

Cheers

 

Prior to the cooler weather, I would see @ 13.5 volts at trip end in PARK

Cheers

 

Maybe the car's 12V charger is like my intelligent multi-stage 12V battery charger which has an auto summer/winter mode. It limits the voltage to a lower value when the ambient is above a certain temperature.

 

so wait... yours doesn't drive up to 80mph when in EV mode and ICE doesn't turn on until around 82mph?

you mentioned leaving your car in READY mode fully charged, I was mentioning that under the thought that you are using the CHARGE feature and not a HV charger to get your HV battery charged. also, the thought of leaving a Prius in READY MODE for long periodfs of time using said ICE to charge the HV battery and how the whole heating and cooling of the block this way on the earlier years of the Gen 4 are prone to head gasket issues in my observations.

 

LOL, No at that speed I loose my license here in New Zealand.

Charge mode does not make sense in my use of the car.

 

understood, so when you charge, you are only charging the 12v? Are you not charging the HV system? Also, which charger are you using for the 12V? You know, when you charge the HV battery, the 12v is also charging right?

i found this out one day charging at a charging station while cooking on my air fryer through the power inverter I installed and didn't have the car in READY mode like I normally do. See the video below.

- YouTube

 

with your 2024 PP,
What voltage does the 12v battery see when the traction battery is charging?
What was the resting battery voltage on the 12v battery just before starting the traction battery charge ?

 

Car had not been driven since yesterday morning. Garage temp about 45 F.

Prior to plugin of charge cable, battery voltage 12.59 volts.



After plugging in charge cable, battery voltage 14.34 volts.



After about 6 minutes charge time, voltage dropped to 13.05 volts. I have seen the voltage at the 14 volt value for times as long as @20 minutes. Traction battery only needed about 90 minutes to get to 100% as battery was about half range - this with a level 2 charger.

After a few hours time post charge cable removal, the aux battery voltage reads 12.64 volts.

Charging the traction battery does charge the aux battery but not to the extent of getting the AGM battery to a full 100% SOC. The 12.64 volts is with the parasitic current draw so it is not possible to use open circuit voltage charts to determine SOC. Maybe someday I will pull the negative cable and compare in situ vs OCV to get a data point.

I have an AGM battery in my truck. Typical trip times in the truck and Prius is 20 minutes or less. Longest trip 3 times a week is @28 minutes. For years, I would put the truck battery on overnite charge to get to 100% SOC and improve battery life. I got 5 years from the truck AGM and it was functioning fine. Felt time was right to replace it earlier this summer as precautionary. I may opt to charge the Prius AGM battery once a month to a full overnight charge as a means to improve service life.

Regarding the truck AGM, Ford programs the BMS to maintain 80% SOC. I deactivated the BMS years ago along with start-stop function.

The UPlus AGM battery along with the Toyota charging system is meeting my expectation of not worrying about a dead aux battery like I experienced this past August with the OEM battery. I have a plug in voltmeter in the 12 aux port. I test the battery occasionally by pressing the start button with foot not on brake putting car in accessory mode. The voltage I am seeing is 12.2 - 12.4 volts which assures me the battery is healthy and sufficiently charged. I have the same voltmeter plugged in my truck to monitor the same battery health data.

Cheers