12v Battery Is Discharging, Re-Charge Now !

I am disappointed that we have this 12V issue in Gen4/Prime. One would think Toyota would have fixed this issue that plagued the earlier generations as well. Surprisingly my 2007 Camry Hybrid (in service from Fall 2006, and has SKS) is still on the original battery. Of course it's a bigger battery than the Gen3 one, and I have also adopted the below measures/steps to try and keep it working for longer:

1. Switch off all electricals (including A/C, headlights, etc.) OFF after placing the car in Park. Especially also moving the headlights switch from Auto, etc., to OFF.
2. Also, I leave the cabin lights set to OFF (as opposed to DOOR).
3. Take the foot off the brake pedal to switch off the brake lights in the back.
4. Switch off the car.

One thing that could potentially mitigate the issue is a larger battery, with more capacity if there's one that fits.

A couple of other things I wish Toyota had done:

1. Charge the 12V as needed whenever the car is plugged-in (even when the traction battery may not be getting charged).
2. Provide a way for the traction battery charger to be programmed to charge to a specific capacity (say 60%) and also a timer to charge for a set duration. I guess one could probably find a sophisticated charger that does these things, I have yet to look.

 

Does anyone know if, during the 3/36 period, Toyota will test and recharge the 12V for free if it gets discharged and the vehicle is taken to the dealer? Or will they charge a $100 diagnostics fee?

 

You know the 12v battery in PRIME and regular Gen4 is now under the hood, not in the back cargo area?

 

Yes, I am aware, but I think the questioner was referring to his 2014 Prius . It's still Gen3 with the battery under the hatch right?

 

Oh, I see, the question in #317. Yes, Gen3 has the battery in the back. I had my Gen3 for 2.5 years, but never searched for the 12v battery. No charging, no jumping, no maintaining.

 

Sorry if this has already been addressed: has anyone tried disabling SKS using the key-fob procedure in the manual (mentioned in the below thread) and has measured the voltage to see if that keeps the 12V in better shape?

Is there a way to disable Smart Key in Primes when going on ...priuschat.com › ... › Prime Main Forum (2017-Current)

 

Yap. Disabled SKS either by the fob or via OBDII using Carista or both, had no perceivable difference in the 12v battery drain over time. It's somewhere in this thread.

 

So, any suspicions on what's actually causing the drain?

 

Toyota is not telling us. Maybe it's their surveillance system linked to Amazon cloud... Who knows.

 

I discovered something interesting about 12v battery charging system in Prius Prime. As shown before, the12v battery is charged from the traction battery when the car is in READY mode. In my previous post, I commented parking the car in READY mode for ~3 hrs replenished the 12v battery very similar to the characteristic of plugging the 12v battery to an external charger for 3 hours.

12v Battery Is Discharging, Re-Charge Now ! | Page 15 | PriusChat

Last week, for the first time I had a chance to drive my Prime on a longer trip on highway. Until now, all of the drive was less than 1 hour continuous drive. I did ~4.5hrs of continuous drive on HV mode. During this 4.5 hours, the 12v battery was charged at high bulk voltage of above 13 v very short immediately after turning the car on and very briefly during the entire trip. The duration of the bulk charge is less than 10 min total. The rest of the time while car is driven on HV mode with mostly with engine, the 12v battery was maintained at about 12.85v. I had only 20% EV ratio on this trip for I was driving over 70mph most of the time. And I only had a smartphone connected to the 12v outlet for charging and USB audio playing with no A/C. Thus the use of the traction battery was not excessive. Certainly the traction battery use besides occasional EV drive under HV mode was not much different from the time I parked the car ~3hrs in READY mode. The 12v battery after the trip was at 12.58v, but after sitting on my driveway for 2 days, it drained to 12.37v. At the point I connected the 12v battery with the external charger. In contrast, the car parked in READY mode for 3 hours charged the 12v battery entire duration at bulk charge voltage above 13v. And the 12v battery after that charge maintained the voltage much longer.

Here is the graph of the 12v battery voltage over time with 4.5 hours of travel in day 1.


Compare above to the graph of the 12v battery voltage over time with 3 hours of parking in READY in day 1.

What I can conclude from this single case study is that a long drive alone is not sufficient to maintain the 12v battery SoC, but it seems a long Park in READY have similar effect as external charging.

 

The Prime won't lock when in Ready. At least mine won't. I wouldn't want to leave an unlocked car on my driveway in Ready. I'm in a very low crime area but still I wouldn't do it.

 

I am not suggesting to keep a car in READY and parked while unattended for 3 hours or longer just to maintain the 12v battery. For that, using a smart charger is far better solution. But just FYI, you can still lock the PRIME while car is parked in READY mode using the physical key. You are correct that the power lock and SKS will not let you lock the door.

 

For 50 years my habit when parked, regardless of how cold it was outside, think Alberta winter, was to turn the vehicle off to save gas. At the moment, with little to no use I have to charge the 12V battery every 5 days. After the charge it's always >13 and after 5 days it's almost always 12.37 meaning charge me.

After reading about leaving the vehicle in Ready mode I'm going to start by waiting in Ready mode. This makes me unhappy because when I have to wait I prefer to leave the vehicle and walk so I can get as many steps in as possible. The downside is I then have to use the charger.

I've said it before and I'll say it again, if I'd known about the 12V issue I would have bought something else. It's a small inconvenience but after 50 years without having to worry about the battery this is NUTS.

 

If practical (garage parked with electrical outlet): smart chargers can be left on indefinitely. They do a full charge regimen, then just maintain it.

 

There was a story I read where a woman left her car plugged in for 2 wks and found her battery dead when she came back home.

Carl Best
"The owners manual for our 2017 model warns that leaving the charging cable connected for long periods of time will cause excessive drain on the 12v battery due to the computer remaining active to check charge status.
The longest we’ve ever left our car unused is about 2 weeks, and it had no problem starting after that."
Plenty here about it.

 

@thymara What does the 12v show if you leave it for 7 to 10 days. If the 12v goes below 12v in 7 to 10 days than the parasitic losses are unusually high. Mine has been at 12.14v and I still didn't feel the need to put it on a battery tender, but I did keep track of how the 12v was cycling both after driving in EV mode HV mode and Charge Mode and after letting the car sit for a couple of days.

 

You are correct about keeping the traction battery charge cable (often called by a misnomer "charger") plugged in for a prolonged time will cause the 12v battery to drain. @Mendel Leisk is talking about a 12v battery charger that connects only to the 12v battery. Most of the 12v battery chargers have maintainer function built-in and after completion of the charge, it will stay as a maintainer to keep the 12v battery healthy.

BTW, I have shown by monitoring the 12v voltage during the traction battery charging with the OEM L1 EVSE. The traction battery charging does maintain the 12v battery somewhat during active charging time, but not much. It does not bring the 12v battery voltage up to full charge.

12v Battery Is Discharging, Re-Charge Now ! | Page 10 | PriusChat

 

Our first plug-in-hybrid was a 2013 Ford C-MAX Energi. If you plugged in the EVSE charger it actually kept the 12 V charged. That sadly is a pretty idiotic design feature to have to choose between charging your HV battery and 12 V battery health....

moto g(7) power ?

 

What a strange way to design a PHEV....

How is this engineering defended?

 

@Bill Norton I doubt there is an engineering justification. I'll submit, without knowing for sure, it might be an economic justification. I, four one realize there is a LOT of stuff going on in these cars today I don't know about and even some of the things I do know about and still don't understand or know why some of them are even added to the new cars.
So far, even with the price increases we all live with - a 12v lead acid is one of the least expensive, easily replaceable parts of the car, comparatively speaking, especially when looking at the overall picture of a few of the more expensive parts the 12v systems are responsible for waking up.

If when looking at solar systems, one of the easiest first lessons to learn, even with current reductions in Li-ion or - LIB if we must Lithium-ion battery - Wikipedia. - is that lead acid is one of the oldest and still cheapest ways to backup a solar array.

Still, not a very good excuse, just what I could come up with on the spur of the moment.