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

Just curious, when you do the charging with the Noco are you simply putting it on the AGM setting, or doing the repair charge?

I ask because the constant current and 14.8V set point you referred to is the repair setting.

 

In gen 3, there is a self-test of the evaporative emission controls for the fuel tank that begins several hours after parking and turning off the car (in gen 3, I thought the schedule was 5 hours after turning off, but that could be extended based on temperatures). I'd guess this is the same thing. The power is going mostly to the leak-test pump, which runs in stages B through E of the test:



The pump can run anywhere from about 7 minutes to about 22, depending on how long stage C takes.

I think we usually use 'parasitic' to mean drains that don't happen on purpose, so it wouldn't be quite fair to call this one 'parasitic'.

I don't think the evap test will run repeatedly if the car is just left alone for a few weeks. I think it'll run the one time, several hours after the car is left there.

 

Posted the below in wrong thread.....

Model:
Prime Premium
Gokhan said: ↑
Ha, what is the 12-V-battery current when the DC–DC converter pulls back to 12.86–12.92 V? And how about at 14.10 V? It has about four voltage settings: 12.89 V, 13.05 V, 13.53 V, and 14.10 V.


OK, here's some data to digest. I hooked up my Topdon Phoenix Lite 2 scan tool this morning. The data streams I recorded were AUXILIARY BATTERY VOLTAGE (ABV) and AUXILIARY BATTERY CURRENT (ABC). The car had not been driven since yesterday morning. Starting battery voltage before READY per my BM read 12.41 volts.

READY mode enabled, scan tool (ST) ABV 14.219 volts and ABC 7.160 amps. ABV stayed constant at @14.2 volts but ABC started to slowly decrease with time to @3 amps at which point the ABV decreased from 14.2 volts to 12.8 volts As the ABV decreased, the ABC decreased and went negative -4.345 amps when the ABV read 12.795 volts. The ABV held steady at @12.8 volts and the negative ABC started to decrease (lower negative current). The negative ABC held at negative 0.5 amps for a time period. Then the negative ABC dropped off and would pulsate from plus/minus current of about 0.1 amps. With time, the ABC stabilized positive @ 0.2 amps with ABV holding steady at 12.8 volts.

I was recording while driving the car. Came to a stop and noted ABV increased to 13.599 volts and ABC now 3.803 amps. ABC would slowly decrease but ABV stayed stable at 13.6 volts. ABV deceased to 12.8 volts and ABC now negative 2.041 amps. With time and ABV stable 12.8 volts, the ABC negative current slowly became less and went slightly positive before I shut the car down.

NOTE: I am unable to correlate times with the data stream frame shots unfortunately. I don't use this ST often enough to be that knowledgeable on how or if it can be done.

OBSERVATIONS:

The ABV as read on the scan tool data stream was in exact correlation with the voltage meter I have plugged into the 12 volt outlet on the center console.

The scan tool shows a stabilized 12.8 volts but a pulsating ABC. See snapshot below.




One other observation. On the upper right corner on the scan tool is a voltage display. This voltage would constantly fluctuate typically plus/minus 0.3 volts or possibly more. Hard to capture. I did note seeing @14.5 volts as the highest on occasion. This voltage reading is from pin 16 on the OBD2 connector which I confirmed with Topdon.

My takeaway is that the charging system (BMS) for the aux battery seeks out and stabilizes at 12.8 volts. The pulsating ABC is most likely from the pulsating voltage that the ST sees on pin 16. I don't have a WD to see how pin 16 taps into and where. I haven't been able to find a data stream that monitors pin 16 voltage. Pin 16 is typically described as battery voltage. So why the difference between ABV and pin 16 voltage ???

From what i saw and recorded today, short trips will definitely drain the battery over time.

I'm charging the traction battery and plan to leave cable plugged in to see how my aux battery reacts. After that, plan to install the AGM battery and do a similar data stream recording.

Cheers

 

Puzzled why the pin 16 battery voltage as seen on the scan tool behaved the way I saw it. The scan tool showed AUXILIARY BATTERY VOLTAGE (ABV) stable at 12.8 volts like my voltmeter device plugged into the 12 volt outlet. Now thinking back, the pin 16 voltage would rapidly flux about 0.2 volts above and below the 12.8 value. So my theory is the ABV is smoothed out on the data stream but the AUXILIARY BATTERY CURRENT (ABC) reflects the fluctuations. The time is did recall seeing about 14.5 volts on the pin 16 voltage display was when the ABV was 14.2 volts. Just my thoughts.

A few additional snapshots. Unfortunately, the scan tool data file can only be played back on the tool. No option to create PDF so I just tool camera shots of several time frames

Cheers

 

Yesterday data was with OEM battery. Hope to get the UPlus AGM installed today and do similar scan tool data record.

Charged the car yesterday and decided to leave the charging cable installed to learn how car battery depletes with time.

3:00 PM. Car finished charging. BM voltage 12.43 volts

3:13 PM BM voltage stabilized at 12.60 volts

9:19 PM BM voltage 12.47 volts

6:15 AM. BM voltage 12.40 volts

So it appears my car is not a candidate for the TSB as I once suspected.

Cheers

 

Installed the UPlus AGM this morning to replace the OEM Yuasa battery. The AGM had been on charge for a week with a Noco Genius 5 charger. Green light steady indicating full charge. Did not measure voltage after charger disconnect. Installed in car and waited 1 hour to ensure car asleep. BM reading 13.01 volts.

Made a 31 minute trip HV mode majority highway driving. Scan tool monitoring AUXILIARY BATTERY VOLTAGE and CURRENT. Stop watch to record time to get approximation of frame recording interval.

INITIAL DATA - READY MODE



5 MINUTE ELAPSED TIME DATA


5 MINUTE 15 SECONDS ELAPSED TIME DATA



MOMENTARY HARD ACCELERATION 17 MINUTE DATA



28 MINUTES 45 SECONDS ELAPSED TIME DATA




30 MINUTE ELAPSED TIME DATA



END OF TRIP DATA




SUMMARY

BM voltage 1 hour after car shutdown measures 12.99 volts.

The transition from 14.2 volts charging to 12.8 volts at the @5:15 mark showed a high battery discharge of around 30 amps. As time progressed, the current discharge decreased to less than 1 amp with 12.8 volts. At about 17 minute mark, I needed to pass a truck on an uphill slope. Hard acceleration and noted that the ABV went up to 13.1 and ABC @ 8 amps for a short period then back to 12.8 volts and current discharge. For about 26 minutes, the ABV was 12.8 volts and the battery ABC showing discharge. This was for the AGM battery. The data I recorded yesterday for the OEM indicated the ABC did eventually go positive, i.e., charge current, with time. That said, the AGM voltage post 1 hour car shutdown was 12.99 volts which is 0.02 volts less than at trip start.

It appears to my thinking that with the AGM battery, the BMS sees the battery at a certain capacity to where it can allow a small discharge current and thus reduce load on the DC-DC converter resulting in better fuel economy. My initial takeaway is that the AGM should perform better for my driving scenarios. Time will tell.

Cheers

 

This is all nice and everything, but have you tried the tests with everything running? AC full blast. Radio on. Charging a phone. Headlights on. I only ask because everything runs off the 12v battery even as its being charged by the inverter.

 

Car batteries are only manufactured by like three companies, according to this video.

It may say Interstate Batteries underneath, but Johnson Controls manufactures them.

 

My EverStart AGM battery from Walmart was made in South Korea by Clarios Delkor. That Project Farm video is several years old. I don’t know if Interstate currently makes some EverStart batteries for Walmart. If so, interesting that Walmart battery warranty better than Costco warranty.

 

The 12 volt aux battery is charged by the DC-DC converter not the inverter which is AC

 

The UPLUS AGM battery has been installed in my 2024 Prime XSE Premium for about a week. Here are some observations to date:

The OEM battery resting voltage after a day or so typically would be 12.3X to 12.4X volts if not charging the traction battery. The AUXILIARY BATTERY STATE OF CHARGE as read from the scan tool data stream was 31 AH. The OEM battery is rated at 45 AH. Typical drive charging scenario would be 14.2 volts at start then dropping to 12.8 volts. Per the scan tool, at 12.8 volts, the current into the battery would pulse between a low plus/negative value so this appears to be the maintaining charge value.

The AGM battery resting voltage has been 12.7X to 12.8X volts. The AUXILIARY BATTERY STATE OF CHARGE reads 46 AH. The UPLUS battery is rated at 50 AH. I don't know if the ECU can calculate up to 50 AH since the OEM is only rated at 45 AH.

Charging scenario differs slightly from the OEM per my observations. When charging the traction battery, the initial aux battery voltage is 14.2 volts for about 5 minutes then decreasing to 13.08 volts for the remainder of the 3-4 hours charging time. I use a level 2 charger. The OEM battery voltage during traction battery charge would also start at 14.2 volts but drop off to 12.8 volts with time.

With the AGM battery, if I drive the car after traction battery charge, the aux battery voltage starts at 14.2 volts but within a short time drops to 12.8 volts. If I drive the car after it has sat overnight and not recently had the traction battery charged, the aux battery voltage starts at 14.2 volts, drops to 13.5 volts with time and then drops to 13.1 volts and stays at that voltage for the remainder of my 20 minute trip. With the aux battery voltage at 13.1 volts, the aux battery current pulses plus/negative low current value similar behavior as the OEM battery at 12.8 volts.

Since the AGM battery has a higher SOC voltage compared to the OEM flooded battery, the slightly higher charging voltage noted seems reasonable.

In summary, the AGM battery is working better for me than the OEM based on the typical trips I drive which are 20 minutes or less. Will continue to monitor. With this experience of the AGM, I have confidence to move my jump starter from the glove box to the rear hatch area

Cheers