Low 12-Volt Battery Apply Parking Brake Securely...

I may have unwittingly caused this after all. I was reading some more posts here about an hour ago, and I read one that said having something plugged into your OBD2 port can drain your battery. I then remembered my Carista* that I used to change some settings. I looked in my car, and, sure enough, it was still plugged in. And, even when the car is off, the red LED on it shines. I pulled it out and it was warm, which means it must create some not wholly insignificant draw.

Then again, it has been plugged in constantly for over five months now. I guess it may have been affecting the 12v battery that whole time. I usually drive my Prime every day, at least twice a day, so that may have kept any problem at bay. Perhaps when I left it parked for almost 20 hours the other day, that was just a bit too long without driving and with the Carista plugged in continuously, and it finally created a noticeable problem. The alarm the dealer installed also pulls some juice when the car is off, so those are two draws Toyota did not intend to be there.

I took a suggestion from @Mendel Leisk and bought a SOLAR BA7 battery tester and I also bought a CTEK Mus 4.3 battery charger (seems like it is idiot proof). I'll use them when they arrive Saturday. I went by an AutoZone yesterday. They checked the battery for me, but said it wasn't charged fully so they couldn't fully test it. I left my Prime in "READY" mode for a few hours last night and went back to Autozone today. This time they told me they can't test batteries in hybrid cars. I explained that it is just a 12v battery, and that they had tested it yesterday, but they refused. So I'm getting my own equipment. I'm also going to get another multimeter. A burglar stole a LOT of tools from me several years ago, and I'm only now beginning to replace some of them.

I'll post again once I've checked the battery and charged it.

*For those who haven't heard of it, the Carista is a device that lets you change some settings in the Prime that you can't change through the menus in the car (like whether the car beeps continuously when in reverse and how many times the turn signal flashes when you just tap and release the lever).

 

I've been looking around these forums and the internet, and it seems that there are no aftermarket alternatives to the factory 12v Prime battery. Is that right? If you had to buy a replacement 12v battery for a Prime, you'd have to get the Toyota battery, and it costs $450?

 

Hi Mendel - Thanks for that. It's good to know someone else is using it. I decided to go with it because the manufacturer claims it is safe and won't fry a car's electronics. A few questions, though: First, do you leave your battery installed in your Prime when you use this charger? Second, why would you use the AGM/Snowflake mode instead of the car mode? Third, how long does it usually take (I know this will vary by how depleted the battery it's charging is)?

(I'm not sure about the cost of the replacement Toyota 12v battery, I just saw $450 mentioned in another thread, I believe.)

 

Hi Elektro - Thank you for linking me to that! I don't know how I missed that thread. So it looks like that Duralast might fit right in with no complications? I guess the issue is that nobody is motivated to try it with our Primes still under warranty. I hate to think I might be relying on a damaged battery (I know that it isn't good to discharge these SLI batteries). I'll just keep carrying my Cyntur lithium-ion Jumpstarter pack around with me. With its 250 cranking amps, it seems like it might be able to fully substitute for the Prime's 12v battery.

 

TESTING
My Solar BA7 ($74.58; link below) arrived today. As an aside note, calling it the "SOLAR BA7" was a horrible decision. It is not solar and has nothing to do with solar power. It is made by Clore Automotive.

I tested my Prime’s battery with the BA7. It read my battery at about 12.25-12.3v, 385 CCA and the BA7's green and yellow lights came on indicating my 12v battery was good but needed to be recharged. So next I moved on to charging it with my CTEK charger.

CHARGING
Based on how charging went with the CTEK MUS 4.3 ($86; link below) went, it seems my battery was more than a little discharged: When I first connected the charger (set to the car mode, not snowflake), the lights for steps 1 and 2 seemed to both light instantly. Then, within a few moments light 3 also came on, which meant it was in bulk charge mode.

The charger immediately determined that my battery is not sulphated (step 1) and would accept a charge (step 2), and went right to the main part of the charging process: step 3 (bulk charging). Within 15 minutes, it was on to step 4 (“absorption,” charging from 80% with declining current to maximize up to 100% battery capacity). It stayed in this absorption stage for over 5 hours and fully charged the battery, giving me the step 7 fully-charged green light.

RETESTING AFTER CHARGING
After the 12v battery was fully charged, I retested it with the BA7 and found it was then putting out 12.9v. The BA7 read 392 CCA and only illuminated the green "Battery OK" light. As soon as I opened a door, the 12v battery never registered between 12.5v and 12.6v (until I put my Prime in READY mode).

I have purchased the dual USB cigarette lighter charger with voltage readout ($12.99; link below; ) so that I can easily monitor the voltage of my 12v battery (when the car is in ignition mode, when I “start” it and when it is running. Because I had a lighter socket installed that can be on when the car is off, I can also check it with the car off. After the full charging of the 12v battery, this dual USB charger reads 12.4v in the stock cigarette lighter plug in Accessories mode, and 14.1v in READY mode (while parked in EV mode, when the HV battery is maintaining/charging the 12v battery). Note that this dual USB charger's voltage readout is accurate. I know that because I checked it several times with the car in different modes, and it always reads the same voltage as what the BA7 reads.

CONCLUSION
From all of this I determined that leaving my Prime in “READY” mode for several hours (I’m pretty sure that the HV battery charges the 12v battery in “READY” mode) and taking several relatively short drives (and full plug-in chargings of the HV battery) was not nearly enough to fully recharge the 12v battery. To achieve the full charge the CTEK charger achieved in just over 5 hours, I presume I'd have had leave the Prime in READY mode (either driving or simply sitting) for at least 5 1/2 hours, and probably longer. And I doubt that the Prime could charge its 12v battery as well as the CTEK since the CTEK has a complex 7-step charging process at varying voltages.

I'm happy with the items I bought for this (BA7 tester, CTEK charger, and dual USB cigarette lighter charger with voltage readout). I don't think I could have tested and fully charged my Prime's 12v battery without them.

(Note: When I get another multimeter, I’m going to check the draw on the battery when the car is off with no load except the alarm, which cannot fully turn off. I’m also going to check it with the Carista device plugged in to see how much juice that was drawing with the car off. I’ll post those results here in this thread, too, for anyone else who might be interested.)

LINKS TO PRODUCTS USED
"SOLAR" brand BA7 car battery and system tester
CTEK MUS 4.3 charger
Dual USB charger with voltage readout

 

Hi Mendel - Okay, I measured the draw on my Prime Advanced's 12v battery when my Prime is off (with no lights or anything on but whatever the Prime normally uses and the KARR alarm system the dealer put in). The draw is about 50-70 milliamps. I suspect the alarm accounts for a significant portion of that, but I don't think I have any good way to turn it off to test that theory. That is much higher than yours, but I suspect that a Prime normally has a somewhat higher draw than a '10 Prius because, from what I've read, newer cars with more systems tend to have higher draws. Apparently 70-90 milliamps isn't unusual on some new vehicles. Systems like Onstar and proximity key sensors account for a lot of that, it seems. I'd be interested to know what the draw anyone else with a Prime Advanced is seeing (especially if they don't have an alarm).

I also tested the draw with the Carista device plugged into the OBD2 port, and that raised the parasitic draw from about 50-70 milliamps up to about 90-100 milliamps (so almost twice as much, which is significant). I also tested a dual-plug USB charger with bright blue LED lights on it (not the one with the digital voltage readout), and it drove the draw up to 200-220 milliamps (with the Carista connected, too)! I had a 12v cigarette lighter outlet installed that can be left on or off when the Prime is off, and, though it is my practice to leave it off, I'm sure I've left it on a few times here and there.

 

I got one similar to yours. It is accurate (I checked it against two other devices). I noticed that when I get in and put the Prime in READY mode, it jumps to about 14.1v. However, while driving around in EV mode, it is often only at 12.8v. When I shift to PARK, it goes to 13.5v. If I put it in HV ECO mode and am going over 40 mph, it seems that it jumps up to around 14v. So I guess the battery is being charged at different voltages depending on how you are driving. It seems to me that a lot of lower-speed EV driving results in the battery only getting about 12.8v of charging, which is going to charge it far less quickly than 14v (if I understand things correctly).

 

Hello Lucifer - Actually, I'm almost certain that is incorrect. On at least some previous PIP Prius models, the 12v battery was charged while the Prius was plugged in and the traction battery charging, but that is not true with the Prime.