I had to jump my 12v battery today - How do I maintain a healthy battery?

I found this post and other related posts to be extremely helpful. Thanks, all. I just got back from my dealer for 12 Mo. service and had them check the electrical system because my 2023 Prius Prime shut itself off after listening to the radio for 5 minutes while waiting for my wife's train. I was told to go to the dealer for this check when I called Toyota Customer Care. Based on the thread here, I plan to tell TCC to change the name of this mode when they call me tomorrow to follow-up on my concern. The dealership says ACC mode is only there for their mechanics to run tests under that setting. So why does Toyota use a term that most (older?) owners would associate with using power without the engine on? And I could find nothing in the Owners Manual warning about draining the 12v. The only thing I did find said, "Do not use the power outlet longer than necessary when the hybrid system is off." which conflicts with the advice I got from the dealer NEVER to use ACC. The previously posted advice to use READY mode instead seems to be spot-on.

 

I'm glad you found my post helpful.

I should add to what I said then to say that I'm no longer using the parked-but-READY trick to top up the 12V battery. Instead, I bought a Noco Genius 2D battery charger, permanently mounted it in the trunk, and permanently wired it (just 2 M6 nuts) to the 12V battery. When I see that that battery is low, I open the trunk, run an extension cord into it, and plug in the charger. I can even close the trunk over the extension cord without apparent injury to the car or cord. I can leave the charger plugged in indefinitely, and not have to think about it.

 

On my Toyota Prius the oem 12 volt battery has the sticker warning ⚠️ stating that the battery can be on a battery charger at no more than 4.2 amps and fully charged in 10 hours.

So my question is, if I have a smart charger, is it ok to keep the 4 amp battery charger plugged in and connected to the 12 volt battery for more than the 10 hours?

 

• "Dashcam plugged into the cigarette lighter is draining the 12v battery (shouldn't be right? Accessories are turned off when vehicle is off)"

Yeah that outlet gets NO power once the car is off. It can't drain. The only thing that MAY cause a drain is if there is some power source in the dashcam feeding back into the 12v and keeping the car awake.

• Second smart key might have been pinging the car, I keep it on the second floor with the car parked directly below

Get a small faraday box to store your FOBs in. This prevents pinging AND as a bonus no one can remotely jack your car using a large repeater antenna. I have one and it's just nice knowing it's that much harder to steal the car.

Another suggestion, get a cig lighter USB thing that has a voltage readout. I use B01M9IKYVH (amazon) and have had it in this car and my last car. This tells me what the 12v system is running at. When the HV is charging the 12v I get between 13-14v. I assume 13v is when it's tapering off. When it's not charging but the car is running it's around 12.7v. I assume it does this occasionally to load test the 12v battery and see if there's significant voltage drop. In my old car, this adapter specifically was about 0.2v off from a multimeter at the battery terminals. So the read out was good. Haven't checked it vs terminals in the Prius though.

 

A smart charger should drop to maintenance charge once the battery is full.

 

if it is a battery maintainer, it is more than safe, it's healthier than not having it connected

 

Yes! This is the one I’ve been using. It’s made by Clore Automotive & rebranded with the Napa brand.



https://www.napaonline.com/en/p/SORCBM612V4A

 

I should have added that the Noco device came with clamps at the ends of its leads. I thought that these would not necessarily be stable enough for a permanent installation, so I cut them off and put on some crimp-on Y-shaped connectors.

 

The battery charger I have shown above has the option of the quick disconnect with the metal
o-ring terminal and that’s what I’m using now. The picture doesn’t show it.

 

I’m using a CTEK 4.3 that’s sim design. With our low usage the car’s connected pretty much all the time. The 12 volt’s been in almost 9 years now; tests like new.

 

I have a Prius Prime XSE and have not yet had my 5,000 service yet and am on my 3rd battery. Before they installed the latest battery at the dealership, I had them give it a full test; the first two batteries tested and failed. The battery passed the test and I approved the install. I then got a NOCO Genius 5 and plug it in every day when any driving is done. I personally don’t have an issue with this as I documented the first failure with Toyota (new buyer survey) and after the second 12 volt battery failure I documented it again with the dealer and also with the District Representative. I have not had a problem since. I still believe there is a parasitic drain but it is no longer an issue when the car is idle. I also have the same NOCO battery charger as you have.

 

hopefully, everyone has a place to plug in

 

I would just leave it on, day after you’ve driven, and leave it on till next use.

 

Right On!

I'm a little late to this issue - 18mo with 2023 Prius Prime XSE and never had a problem - UNTIL TODAY; No start after a week of no use.

The manual says "if not used for 2-3 months ...", so how does a week sitting with the hybrid battery at 88%, (no Drive Connect), result in a 12v battery that will not allow the car to progress to "Ready"?

No I'm not going to connect a trickle charger every night, since I haven't a clue how long till the next time I will drive the car, but I know it is not going to be 2-3 months so I should not have to do any "storage prep".

I jumped it and drove around for a bit in HV mode, parked it again and the 12v battery is reading 12.05 volts. I set up a service in two days, so we'll see what the dealer has to say about it. If they don't replace the battery, I'm not jumping it anymore - I'm calling the Toyota Roadside, over and over till they replace the battery. My 2009 Prius didn't like to sit at the airport for three weeks when my battery was old, but 7 days is really weak for an 18mo old battery.

 

I threw in the towel on not babying the 12 volt. We’re doing about 3k kms yearly driving now, typically longish drives, but very intermittent. I do have the luxury of a garage with AC outlets, and I’ve got a charger, and it came with a wiring harness that can be permanently connected (which I did), makes connection easy.

maybe batteries should be more robust, but here we are. I don’t want to be constantly thinking of reasons to drive, near purely for the battery; it starts to get absurd. I’m pragmatic, keep it on a quality charger, over nine years and still going.

 

Was the car plugged in for that week? The standby drain on the 12V is higher when plugged in and not charging. From other statements in the manual, that not used for 2 to 3 months is with the car unplugged.

Your use cycle is outside the parameters cars are designed for. The engineers expect a car to be driven far more often. Needing a battery maintainer when doing nearly 10k miles a year is when it gets absurd.

 

The Owner's Manual mentions the 12 volt battery possibly running down, references another section, then continues, saying that the hybrid battery may become depleted if the car sits, for the aforementioned "2-3 months". It also notes that protracted plug-in of the hybrid battery charging cable cable will deplete 12 volt battery charge faster. Commencing on page 80:


And continues on page 81:

 

I had a weird incident where there was power from the 12 volt and then for a few minutes or so, I reopened the door and 13 volt power was out. Trunk will not open and no lights ! Closed all the doors….

about to jump the car and then when I opened the car, everything is back on! Like nothing was ever wrong !

its beeen fine but wondering if I have a short somewhere…..

 

My $1000 phone, watch, and iPad all need me to plug them in and manage their batteries - acceptable.

My two $500 and $700 robots have climbed on/off their docks as they need to stay alive for the last 7 and 6 years - I built them and wrote the code with love. Acceptable result.

My $40k car with the latest tech built and programmed by a bevy of people smarter than me needs me to jury rig a $27 charger and remember to plug/unplug it to keep it healthy- that's not acceptable. I used to park my 2009 Prius at the airport for long business trips or vacations with no worries (except once when it needed a new battery).

I love my 23 Prime, but no, this is not acceptable for a $40k tech toy, that I bought to be relied on to take me away when a cat 5 hurricane is barreling down on south Florida.

 

I agree, but whatyagoingtodo?