WHY NO 12V Battery Charging Instructions in Owners manual ?

Yes, the underhood jump point can be used to hook up a battery charger. For AGM batteries, a good automatic charger can be used. Toyota naturally recommends a very fancy-schmancy professional wheeled charger that costs many thousands of dollars

The Prius 12 vdc battery is quite small and easy to discharge. If the car is left in Ready a lot, eg as a taxi, the battery should last a long time. Short trip use, probably not

I used a VDC Battery Minder on my '04 Prius and now on my FJ, with excellent results

BatteryMINDer® Plus 12 Volt 1.33 Amp Charger-Maintainer-Conditioner (Desulfator) | All | Battery Chargers by BatteryMINDers.com

I used the supplied ring terminals to hook it up directly to the battery. Here is the installation

 

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New guy here, so be gentle.

If you open the fuse box under the hood, then remove the yellow (20 amp) fuse on the right-hand side of the two rows of fuses, you can leave the car unattended without fear of parasitic drain from your clock, etc. I'm thinking about installing a "just-in-case" switch to control whether that fuse is active or not.

I will also install either an S.A.E. connector or a Powerlet recepticle, directly to the battery terminals, in order to attach a BatteryTender (2 amp) charger; perfect for keeping the 12 volt battery up to speed.

Marshal

 

I just got back from my dealer - they were great - I got the reverse continuous "beep" and seat belt continuous "beep" disabled. They also changed my remote so one click opens all doors. The rep said that the resting voltage for the 12 volt battery should be about 12.2 volts. Keep in mind that's a test done after the car has been sitting awhile and with NO accessories on (A/C, radio, etc.). I'm not sure what a healthy battery would read with a load, maybe someone will chime in.

 

The reason that the jump point is not listed for recharging your battery is that Toyota does not recommend recharging in that fashion. They want you to disconnect the battery, or better yet, remove it entirely. They take this stand to avoid liability if your charger zaps the car's electronics or causes the battery to explode. Don't expect them to ever recommend anything that increases their exposure to liability.

Tom

 

Better check that address again. Its Torrance, California

 

No danger of overcharging or zapping electronics with a small solar panel. I'll have to run that past Toyota Canada for their take.

 

These 12V jumping instructions, front and back, including how to open the hatch when the battery is dead, are part of my salesman's delivery spiel. This very first part, even.

I take it this is not universal?

 

12.2V when the car is IG-OFF would mean the battery is ~50% charged.
Battery Tutorial | BatteryStuff.com

Although a battery producing that voltage will allow the Prius to start, the battery is not fully charged.

A new 12V AGM battery out of the box will typically measure 12.8+V.

The Toyota TSB regarding battery charging recommends that the 12V battery be removed from the vehicle prior to charging, as a safety measure. I agree with Tom that it is unlikely the owner's manual will be edited to recommend charging via the jumpstart terminals, although the OP found this to be a satisfactory process.

The concern is that the battery charger may have a failure and produce excessive voltage which would damage the battery and electrical system.

 

Hmmm. I wonder the rep was handing me some BS. We tested the battery after he disabled the reverse and seat belt beeping. Admittedly, the A/C was on during the process so maybe that took the battery down a bit. Then he turned off the A/C (we were in accessory mode) and got those readings (12.2 volts). This car is only a month old so I would be surprised if the battery was already wearing out. I don't run accessory mode so again, it would have been nice if Toyota would have incorporated a 12 volt battery display somewhere in the dash cluster.

 

There are "branded" battery maintainers that are, essentially, a Battery Minder or Battery Tender device without the desulfation mode.

Eg: John Deere, Harley Davidson, etc

These are full automatic, and can be left on 24x7 with no danger of overcharging the battery. A conventional "trickle" charger should NEVER be used continually, they can easily ruin a battery

The rep is full of s***. At that voltage, as Patrick stated, the battery is <50% charged. Modify that statement to "12.8 volts" and I would accept it

Evidently not, but it SHOULD be!

Yes, that would be a good idea. My FJ Cruiser has a voltmeter

But no oil pressure gauge. That could have easily fit where the useless Inclinometer is up on top of the dash

I suppose an FJ Cruiser might one day have to do an approach to a runway, and there would be need for such a gauge

 

This thread inspired me to get out my multimeter and measure my battery; here's some numbers for you folks to chew on. For some background, my Prius was manufactured in January, and I bought it mid-March with 7 miles on it. The battery hasn't had anything in particular to deep discharge it, so it should be in good health, and it had a good amount of driving about 20 hours ago, so it should be fully charged.

With the doors closed and everything off, I measured 12.50V. I measured again with the hatch open (12.45V), and hatch open with interior lights on (12.32V). In accessory mode, it measured 12.17V, though the diagnostic screen on the Nav only read 11.5V. Turned "On" (aka press the Power button again when in Accessory, not Ready), it was 12.05V. In Ready, it jumped to 13.80V, though I only measured for a few seconds so I could turn it back off before the engine started, so it might stabilize at a different voltage after a while. When all this was done, it measured about 12.30V with the doors closed and everything off, though after three minutes or so of sitting, it was back up to 12.50V.

What can you get from this? Well, first, the voltage you measure will vary quite a bit based on what is on in your car when you measure it. Most people probably won't be measuring it with everything off. For that matter, I didn't throw my key across the parking lot to see if it would make a difference if the car couldn't sense me nearby. Second, the nav's voltage sensor is either cheap and inaccurate, or they designed it for the purpose of measuring the nav system's power rather than the actual battery voltage; that 11.5V could be accurate, and the system is losing the other ~0.67V in resistive losses in the wiring between the battery and nav system. Or perhaps the nav system gets regulated power to reduce the input range it has to tolerate. I really have no idea there - I just know that it's not an accurate measurement of your battery's true voltage.

I did measure the voltage at both the battery itself as well as also comparing to the positive terminal under the hood; they're the same, and undoubtedly connected with fairly heavy-duty wire if they expect it to be used for charging/jumping.

Also, it's not really possible to know how charged your battery is by looking at voltage alone. The voltage/discharge relationship varies not only by battery chemistry and manufacturer, but also from battery to battery. Add in the fact that a load will affect the voltage as well (and this too will vary by battery), and it's just really hard to tell what's going on in your battery by voltage alone.

Personally, I wouldn't be terribly worried about a battery that's over 12V. In any case, help usually isn't too far away if you find yourself with an unexpectedly dead battery.

 

As an aside, when I was doing these measurements, my elderly neighbor came home with her brother. He identified himself as somebody that worked on transmissions, and advised me at least a half dozen times to not even look under the hood, as I was sure to kill myself by doing so. And he hadn't even seen my multimeter or anything. I had to resort to the "I'm an Electrical Engineer, I know what I'm doing" defense.

(Incidentally, that's the same defense one of my former coworkers used just before attempting to measure voltage in a light fixture with his multimeter accidentally set to measure current instead. Which created a very, very large zap. Luckily, he's not a former coworker due to death or injury, just changes in employment...)

 

macman408,

Thanks for taking the time to take the measurements and make your post.

One additional point; posters have found that the no load voltage of their
12V battery can be greatly affected by whether or not the battery was fully
charged by the dealership during the new car pre-delivery prep.

This suggests that it would be a good thing to get a metered voltage
reading before taking ownership of a brand spanking new Prius.

I seriously doubt that many stars-in-their-eyes new owners are aware of
this little wrinkle. I also suspect that most dealerships would come with all
kinds of BS reasons why it needn't be done.

 

For low amperage charging you can use an extension cord as a simple extender to the charger cables.

If there are jump-start connections, in what way could they create any nightmare situation? The standard technique for designated jump-start terminals in a 12V auto system is to connect another 12V battery to them.

But perhaps as an attorney (who was frustrated by my attempts to out-reason him on a subject that I came to him for help with) once said to me over his shoulder whilst walking away, "There is no solution to the problem."

 

Yesyes, hooray for $5-$10 per gallon fuel prices.

 

Sorry to arrive at the party late. When my 2nd 12v battery crapped I was able to get the car up & running after a few tries. It wouldn't hold a charge so the car did its impersonation of a door stop at the Service Writer's desk. I don't understand why the HV battery can't be used to boot the car when the 12v fails. The additional parts probably cost $0.98.

My V-AT has sat a lot longer than 3 days & no battery problems. If your voltage readings are low get the battery swapped out under warranty.

I checked the voltage readings with my ScanGauge when I took delivery because I was concerned over the length of time the car sat on the lots. The numbers were good.