12v Question / Infrequent Driving

As others have said, the dealer will rip you off.

These are really easy to use. A 'permanent' installation for a plug in one just means finding a spot under the hood where the clips can reach the battery while being as far as possible from the engine and exhaust. Then use cable ties, tape, velcro, mini bungees, etc. to keep it place.

Solar one can be a little trickier. You can't use one that plugs into the 'lighter' outlet, as new cars turn that off when shut down. So it means making connections to the interior fuse panel, or running wire through the firewall. If uncomfortable doing yourself, a stereo installation place should do it for far less than the dealer would.

But I don't think you will need one, and there is at least one reason to wait before installing one. New 12volt batteries can be defective, and they should be covered by the bumper to bumper warranty. Using a battery tender can mask the fact that the battery is defective until outside the coverage period.

If you can't risk getting stuck with a dead battery, a jump starter battery pack can looked into. You won't need one powerful enough to start a V8, and they can be used as back up power for phones and tablets. Ran a laptop off mine for a good chunk of time once.

 

I would consider a jump starter to be just as important as a spare tire.

Oops.....maybe not the best example.

(I've never bought a car without a proper spare - and probably never will!)

 

My ~$20 front mounted 10 watt solar panel is very simplistic in both mounting and electrical hookup, it has worked perfectly since it was mounted.

Best case scenario = it adds a slight 12v charge* per 24 hour period.

Worse case scenario = it hold its own, meaning no 12v loss* per 24 hour period.


Rob43

* It needs to be parked outside in daylight conditions for at least a few hours per day.

 

If you can tie your shoes...you can do this.


Rob43

 

Your call....but here's the thing.
If you take your car out for a spin once a week this just SHOULD NOT be a problem otherwise you should seriously reconsider the decision to buy the car....or perhaps ANY car.
Any car that cannot be parked for a week at a time between even short drives is what we automotive enthusiasts often call...a piece of crap.

But....I get it.
Some people do not like to DIY.

Here's what I would do if I woke up in your shoes:

1. Give you your shoes back.

2. If you're GOING to buy a new Toyota, buy the new Prime. Even if you never charge the traction battery, the incentives will pay you back in higher resale value.

2.1 Drive the Prius for an hour or two, and then put a reminder in your iPhone to think about all of this in about a month.

2.2 (IMPORTANT!!) post pictures in PriusChat.

3. Go to the Amazons and get an automotive jump pack for about $60. You do NOT need something capable of cold cranking a Mack truck.

4. Charge it.....and read the instruction manual both for the charger AND for jump starting a dead Prius Prime.
Put the jump starter in a storage compartment in your car and set a reminder in your phone to check on the charge level in about 6 months.

Repeat step 4 above varying the periodicity more or less depending on the state of charge for your jump pack after 6 months.


Good Luck!

 

If you are comfortable with jump starting a car with that, you can install a battery maintainer.

Installing a solar one becomes tricky because you need to find point to hook it up in the cabin, or find a spot to run a wire through the fire wall to the battery. For a permanent install, you'll also want to hide the wires. I say that assuming a solar powered battery maintainer's panel isn't intended to be left out in the elements.

@Rob43 system above was DIY using a panel that can go outside. I think there is a thread covering how he did it.

A simple solution, if you are still uncomfortable doing it yourself and don't need a permanent installation, is to get a solar maintainer that can plug into a 12v outlet, and have a car stereo place install an outlet hooked up be on when the car is off under the dash. Then you can plug the maintainer into that, and through the panel on the dash while parked.

 

5 days ago I drove my Prime 412 Km, all gasoline as no EV available. Today my 12-volt battery was at 12.3 and, since the preferred limit is 12.4, I've charged the battery. Had I known when I bought the Prime that i was going to have to charge the battery every 5 days I'd have acquired something else. Not only do I have a trickle charger but I also have a jump pack. I have the trickle charger because I had a V but Prius is the only vehicle I've ever owned, and I've had my share of 6, 8 cylinder models from multiple manufacturers, that I've had to resort to the extremes required to guarantee the Prime will not leave me stranded thanks to a 12-volt battery problem.

This situation is just plain nuts.

 

Something that would earn Toyota some brownie points:

Have in the car a flash drive that stores all currently volatile memory, and automatically/seamlessly disconnect the 12 volt whenever the car is turned off, or at least make that a user selectable option. Subsequently when starting the car, it would quickly reconnect the battery first.

A disconnected battery is way more resilient, has next to no loads.

 

What powers the reconnection?

With increased hybridization of the fleet, Hyundai's solution on the Ioniq is more likely. A portion of the traction battery is used instead of a separate 12volt. If it is ever too low to start the car, you push a button, and it gets a quick charge from the rest of the traction pack.

 

Okay. So. I've read a few threads on this topic and the info seems a little bit different (or I'm just dense, which is also likely).

Color commentary: I bought the Prime for my son, whose need for a car and his living situation changed with Covid. So the car is not driven often at all. We already have 2 other cars and work from home so even when we do drive it isn't far. I really don't want to have to drive around aimlessly for an hour a week, even though the solitude might do me good.

So...I had read elsewhere that you don't even need to drive the car to charge the 12V, that you can just put it in Ready and leave it for an hour or so each week. I "thought" this meant the ICE had to be running to charge it (bc elsewhere I read that the main battery does not charge the 12V). So I had been been turning off the EV to get the engine going.

From what I read here, it sounds like I can just set it to "ready," leave it in EV so I'm not polluting and paying for gas, let the main battery charge the 12V and use my free electricity (solar panels!) to charge the main battery from time to time. (But only charging the main battery to 2/3 since you aren't supposed to leave it at a full SOC for extended periods.)

Do I have that right?

Color commentary: A while back I thought that I had run the 12V down to nothing by leaving it sit too long. I thought this bc the ICE would not come on when I drove it. But now it sounds like the 12V did have enough charge since the car would go into Ready and I could drive it in EV mode. It just threw me bc the ICE never came on like it did on my old Prius. Since it is my son's car I had not fully educated myself and did not know how to switch from EV to Hybrid mode... I'm guessing, had I known that, then the ICE would have come on and I would have calmed the heck down. Does that also sound right?

 

If you’ve got a garage with AC outlets get a smart charger (4~ amp), connect and leave it hooked up.

 

Thanks for the response, but but but... my Tesla is in the garage.

I've had a motorcycle on a small battery tender for years and that has worked great. Bought one for the Prius but when I opened it up it said not to use an extension cord. I use an extension for the motorcycle but since this new battery tender is larger I was hesitant to ignore the instructions. Not to mention I'd need to run the extension from inside the garage, which would mean the garage door would be sitting on the cord...

So I'm still wondering

Is that a reasonable solution for now?

I'm too much of a newb to post links but what bought from Amazon was
Battery Tender 3 Amp Charger and Maintainer: Switchable 6/12 Volt, Fully Automotive Battery Charger and Maintainer for Cars, SUVs, and Trucks - 6V / 12V, 3 Amp Charger by Deltran - 022-0202-COS

 

Maybe look into on-board chargers, where you run a male plug out the grill, sim to block heater.

NOCO Genius 2D is one example. It’s wires are abysmally short though, one or the other end would likely need some extension spliced in, likely the AC cord. And the AC plug doesn’t come with a cap.

 

There is no need to charge a lead acid battery for 1/10th of a volt. Subject to temperature, a 12v lead acid battery with an 80% charge has 12.42 volts. 70% charge shows 12.32 volts. 60% charge shows 12.2 volts. 100% charge is 12.6+ volts. 40% charge is 11.9 volts, and that's still enough to power the electronics to get the system going. Lower voltage probably works as well; we don't know the lower limit.

If one wants to connect a battery maintainer (automatic trickle charger), there are cables available with ring terminals on one end for connection to the battery and an SAE connector on the other end to plug the maintainer into. There's no need to open the hood if you can find a good way to bring the SAE connector out through the grille.

If one knows that they'll use the Prime very infrequently, there are manual battery disconnect switches that can be installed on one battery post. They're either a knife switch or a rotary switch. All it takes is to open & prop the hood, open the switch, close the hood, and the battery is isolated. Close the switch to go the next time. The battery will self-discharge very slowly when it is disconnected from the car's electronics. Data like preset radio stations will be lost.

About extension cords...there's nothing wrong with using a good one correctly. There is a lot wrong with using a bad one. It's easier for the product maker to write a prohibition against extension cords than to trust the unwashed masses to use one correctly.

 

I totally agree. I was concerned when my Bluetooth battery monitor showed that my Prime was at 11V5. Not only did it start, it didn't even complain about a low battery. Another time, I actually captured a drop to 10V8 at the moment it started. No complaints from the car.

It's also worth remembering that there isn't an accepted relationship between voltage and state of charge. You can only use it as a guide.

 

Almost every day I'm stunned by the amount of misinformation about the Prime that gets bandied about the internet as fact and leading all sorts of people fo making assumptions that just don't make sense.

There's no reason on earth not to be able to use a good extension cord on a battery maintainer. Just make sure the plugs stays dry.

If a Prime didn't charge the 12V with the ICE not running, no one would buy one. In fact, no hybrid on the road that I know of needs the ICE to run in order to charge the 12V battery. That would be an incredibly dumb engineering decision for multiple reasons. I wonder how many times I'd be dead on the roadside after driving 100-150 miles in one week w/o the ICE ever coming on.

Just put a smart charger on it like you would with any car because, guess what, it has the same kind of lead acid battery as any other car.

 

As it turned out the weak 12v battery issue is not specific to Prime. My son drives Honda CR-Z. The car is a weak hybrid, Honda calls it IMA (Integrated Motor Assist), and unlike Prius, it requires the engine to be running all the time. The battery and electric motor merely assist the engine power output. The car comes with a regular 12v battery under the hood, but like Prius, it is normally used only to wake up the car's computer and hybrid system. The actual cranking of the engine for staring is done by the traction battery. The 12v battery is charged from the traction battery via DC-DC converter just like Prius. There is no alternator like a regular ICE car. In that sense, it is similar to Prius but one difference is that under certain circumstances such as very weak SOC in the traction battery or extremely cold temperature, the 12v battery takes over the starting function by cranking the engine. The problem is that the battery is tiny, and has only 340CCR. And the car's DC-DC converter does not efficiently charge and maintain the 12v battery. This often results in a very neglected drained 12v battery. Since the car is able to start with an even under 11.0v battery with low SOC as long as the temperature is warm and the traction battery is healthy, one often finds out the dead battery when the temperature drops down to let the 12v battery to take over the starting function or when traction battery is weak and dying. My son recently experienced this when the temperature hit sub-zero. After diagnosing the 12v battery, it was determined that the car needs a new 12v battery. I changed the 12v battery with a new one purchased at a local NAPA ~$100, not a big deal except scrambling to find out the Radio Code to reset the OEM in dash radio. But it turns out, this was the third 12v battery in this less than 6 years old car.

 

That effing Honda radio code... utter cargo cult. Good tactic is to stick a label with the code on the end wall inside glove box.

Is it just me, or has the price of quality smart chargers gone through the roof, since March 2019?