Charging/maintaining the 12v battery

I'm not sure if there's any sort of service light that comes on for the 12V battery, someone else will have to answer that. But the battery is charged through a converter that sits between the high voltage system and the 12V battery (to convert that voltage to the appropriate level). As far as i'm aware, no regular maintenance needs to be done on the 12V battery.

 

The 12 volt battery is held at 13.7 to 14.0 volts whenever Prius is in "ready", depending on whose voltmeter you believe. Further maintenance consists of not discharging it when off (widely discussed turn off the interior lights and SK/SS). I found negative terminal corrosion on my replacement battery in 2001 Prius, so someone who is really looking for maint to do, might clean and grease the connections. This type of battery does not allow you to add more water, so cross that off the list.

When my 12 volt got low, the obvious symptom was that the "boot up" happened unusually slowly. I would expect similar in the new model Prius. If you measure "off" voltage at the underhood jump points below about 11.8, you are going to be battery shopping pretty soon.

 

<div class='quotetop'>QUOTE(finally_got_one @ May 5 2006, 01:36 PM) [snapback]250321[/snapback]</div>

The Auxiliary Battery isn't a cheap thing, a 28800-21180 (part number) is only$152.57.
Mine got discharged, cataloged as "customer missuse/abuse" by the mechanics at Atlantic Toyota in Amityville, NY.
There is NOT a maintenance required besides of keeping the top contacts clean like any other type of battery.
Long story short, after a month of a lot of BS by their mech/tech dept, an H ECU was replaced and all problems are solved by now, this isue was terminated few days ago.

 

The constant charge voltage from the converter is great for vehicle electronics, but is IMO sub-optimal for lead-acid battery life.. Although there is a "sense" lead at the battery terminals that instructs the converter to increase its output voltage slightly when the battery is very low, you're only going from 13.8 to 14.0, so for all intents and purposes, you can treat the charge method as fixed voltage.

A fixed-voltage charge *never* fully charges the battery, especially if the voltage is on the low end of the range; lead acid batteries like to stay fully charged and chronic under-charging can lead to sulfation and shortened battery life, which I firmly believe is what is happening on many of the Prius 12V batteries.. Even at the high end (14.0V) of voltage output, the effective charge rate is very slow- when I got my car back from the body shop after 2 weeks (someone rear-ended me which necessitated a bumper replacement), the 12V battery was quite low due to just sitting in the shop for that period and this is the only time I've ever noticed the converter outputting a boosted 14.0 V charge voltage; usually it outputs only a steady 13.8V. While the converter was outputting the boosted voltage, the HV battery current at "steady state" (vehicle on, engine at idle-stop) went to about 3.8A vs it's usual 1.6A, (which actually had a noticable effect on mileage during that time), and it took 2 days of driving (roughly 1 hour 45 minutes per day commute) plus 16 hours of sun over the two days while parked on my 15W solar panel before the converter voltage and HV current went back down to their normal levels, which suggests to me that the 12V battery is chronically in a partially discharged state, and that it will likely never get fully charged with most typical daily commute cycles..

When I replaced my battery a while back, the OEM Toyota battery came out of the vehicle with significant case bulge and depressed terminal voltage, a classic sign of sulfation.. When I took it out and hooked it to my smart charger, it immediately went into desulfation mode (note that I had to take the battery out of the car and disconnect it from the vehicle; with the vehicle still connected, the vehicle drain prevented the charger from seeing the true state of the battery and it just went in to a slow rate charge program).

My new battery is an AGM (absorbed glass mat, so no electrolyte sloshing around) battery meant for a Honda Civic- it is almost the same width as the original battery, but is taller and longer and it also has a significantly higher capacity than the OEM battery. To maximize the life of the new battery, my maintenance routine for the new battery is based what we use for the battery packs on telecommunications equipment (eg, the battery packs that run the cellular base stations), which typically last for 10-15 years. This routine is to disconnect the battery from the circuit (ie remove it from the vehicle) every 6 months or so and load test it to ensure that it's still good, then apply a boost voltage (these systems are normally 24V and 48V systems that use multiple 12V batteries in a string, but the charge specs in both cases translate to the equivalent to a boost of 14.75V per battery on a nominal 12V system, the voltage is pulsed vs constant to minimize gassing) to ensure full charging. Manufacturer specs and our testing on the telecom systems shows that without the boost charge, only charging at a nominal 13.6V will at best get you about 85% of rated capacity on the batteries, whereas starting at the boosted voltage will get you to 100% of capacity every time. Most interesting is that it doesn't seem to matter if you let the battery "trickle charge" for an extended period afterwards- once the current drops and the battery believes that it is "charged", you don't get any significant increase in capacity by leaving it connected to the charger; it's the initial charge voltage that makes all the difference.. Now granted, telecom batteries and car batteries do have some differences, both in construction and cycle use, but the chemistries are fundamentally the same and my experience shows that they do behave similarly enough that you can extrapolate performance of one to the other..

So again, about every 6 months or so, the battery is taken out of the car and tested and pulse-charged overnight on my smart charger. During this time, I hook up a small gel cell to the car to maintain the car's electronics, so I don't lose the MFD and ECU settings. I also take the time to clean the battery as well as the fender well where the battery is normally installed to ensure that there's no spilled battery acid, etc that could corrode the car from inside out... Following this new routine, I fully expect the new battery to last "the life of the car"..

 

Thanks for all the info C4! What are the specs/source/price on the Civic battery? Is it vented? I actually "crossed that line" and am now using a 28 AH unvented SLA.

Did you see the other recent message where I gave links to Conicelli as a source for the "apparently-OEM" battery? $70 classic, $107 new Prius.

 

<div class='quotetop'>QUOTE(c4 @ May 7 2006, 01:06 AM) [snapback]250992[/snapback]</div>

C4, your technical explanation by the experience on batteries is very good and extense, but let's remind other members that the original 36k miles/3 years is a warranty in our cars and any defficienies that our vehicles develop are cover by TOYOTA service. So really is NOT a maintenance isue by the regular drivers.
Unfortunatelly you, C4 and other members to, keep forgething to fill your profile adecuatelly, we do not know what type of vehicle you drive and where you are located to judge by your very interesting comments and technical savy.

 

<div class='quotetop'>QUOTE(c4 @ May 7 2006, 12:06 AM) [snapback]250992[/snapback]</div>

I've noticed the same thing with my 2004 Prius as well. I park in heated underground parking at my condo, so whenever I boot up, the Auto headlights turn on, then would really dim as the coolant pump started up.

At my hobby farm, I have VDC battery maintainers hooked up to my old Ford truck battery and my tractor battery. I know you're not thrilled by the VDC battery maintainers, but a couple of years ago I got 4 of them at a great price at a local liquidation. So I might as well use them.

When I was gone overseas last December for the entire month, I removed the 12 v battery from my Prius and left it hooked up to the VDC in my condo unit. When I returned, I noticed an immediate difference: when I boot up, the headlights barely flicker when the coolant pump runs. Of course, I had to redo my radio presets, "normalize" the windows, etc. The biggest PITA was crawling into the back of the car to manually release the hatch.

Due to recent work changes, I anticipate being away a lot more. I used the VDC ring terminal kit to hook up directly to the battery, and can plug the VDC into a maintenance plug near the ceiling where I park. I can just reach the plug without needing a ladder.

My recent trip overseas I left the car plugged into the VDC. When I returned it immediately booted up as if I had never left.

 

Evidently the ONLY ways to charge the 12 v battery is to either expose it and put it on a slow charger or drive the car.
I had some surgery and couldn't get around for a couple of months but had the car started at least once a week in the garage.
When I was able to drive, the 12 v battery had finally become totally discharged and wouldn't start. I had to get a jump start and drive it about 50 miles to recharge the battery.
Lesson learned.

 

You don't need to drive it to charge the 12v battery (constant voltage dc-dc converter). Just leave it in ready mode for many hours.

 

You can also charge from the jump point under the hood.

Tom

 

I was using external accessories plugged into the Prius 2004 cigarette lighter. I was parked with the system turned on. When I quit I could not start the car or open the trunk or run the windows.

I disconnected everything and let it sit for awhile and the 12v battery recovered enough to let me start up. Then I drove around to get it back a little.

Question: Since I had another 12v battery nearby and could plug that battery back into the cigarette lighter, could I have used this method instead of jumpering the battery directly?

Is that connection direct? Would there be a fuse in the way that might blow? Would it have worked?

Thanks.

 

I believe one of our great techs mentioned that there is a diode in the accessory plug in and the 12VDC bat will not charge that way. It's only output.

 

Nope, no diode: a relay. When the car is off the outlet is inactive and cannot be used to jump the car. A one-wire mod will make the outlet active at all times so it can be jumped, but then of course it would be possible to *drain* the battery through that same outlet...

Almost certainly rbryan13 did not have the car in Ready and in Park (in which case it would have started itself as needed to keep all the batteries charged up), but in ACC.

 

Hello,
Is there a problem with Prius battery life? Seen lots of posts here concerning batteries gone dead because of extended
absence but not alot of complaints otherwise. This car has higher than usual standby drain. Also most people don't seem to understand once you put a good drain on these little batteries they sulfate quite quickly and and that sulfating continues
until the battery won't charge anymore no matter how you maintain it from there. Unless of course they have a desulfating charger like you and get the charger on there quick and might save it before its to far gone. They work well if the battery has not been dead for days.


You seem surprised with the issues you had after the battery was severly drained. Sounds normal to me.
A cars charging system is not designed to boost charge a battery.
A flat battery pulls alot more current than the charging system usually see's. Its designed to maintain a charge. Thats why your car's Inverter and HV pack suffered when it had to re-charge such a low battery after the bodywork incident. Exactly what I would expect.
But using a maintaining charge over the lifetime of a healthy battery is the correct way to do it.

Most cars including this one have a real good regulated charging voltage. Typical is 13.8 to a high max current draw to 14.4 .But overcharging is alot more detrimental then undercharging. Overcharging boils the electrolyte distorting the cells and case. That cannot be fixed by any means. But 13.8 is not undercharging. Thats right on the money. Thats what my car's charging voltage is. When I start it up after a 2 day rest it starts at 14 volts and then settles down to 13.8. I would be concerned if it did anything else.
Thats not undercharging.

If the Prius battery was constantly undercharged it would stress out the traction battery resulting in a impact on gas mileage. Many people complain about there gas mileage with an aged battery on this forum.

So my point is I respectfully disagree with you about the undercharging. As you state that creates sulfating and battery life would be highly shortened and thats just not the case. These little batterys would not last there 3 years under that condition.
I'm on my 3+ years on the OEM battery and no issues. It holds a charge perfectly. But....kill it just once all bets are off.

But I do agreee with your maintenance plan though.

You will double the life of your battery hooking a desulfating pulse power charger to it once in a while but that has nothing to do with the Prius undercharging the battery.That just disolves the sulfate crystals all batteries get over time and very smart.

And as far as the original poster I would check the battery once a year and grease the terminals and look at the case closely and surrounding area and make sure its not cracked or sweating anywhere especially if you live in frigid weather. I aslo removed the main ground bolt right there and sanded the pad a little and covered it all in synthetic axle grease and bolted it back in. Seen some posts about corrosion there.

 

my ( Toyota) dealer put a 12v battery in that was not for a Prius. The electrics played up and they are replacing the battery for a Prius one - could the electronic circuits have been damaged? any way of knowing, other than waiting to see if they play up again?

 

I just had my 12v battery replaced yesterday. The cost of the battery was $196, labor $68 and towing $95. Total with tax was $363.
Interesting note is that in order to have my car towed, the tow truck driver had to use a hand held battery charger to give the car temporary power so I could shift the car to neutral otherwise the car could not be towed. Also, all settings appear to have reverted back to factory settings. The navi has no previous addresses, the reverse now beeps again, etc.

 

Not really, most batteries in most cars last about 4 years, 12v Prius batteries last about 4 years.

There are differences however.

1) The symptoms of a dying Prius battery are different than normal. Most cars crank slower when the battery is dying, the 12v battery in the Prius only starts the computers, the HV battery starts the ICE. Decades of experience may be lost as you learn the new symptoms.

2 and 3) Since the 12v battery does not start the ICE, Toyota made it small with nonstandard posts. A smaller battery is more at risk to leaving the dome light on, or a door ajar. The nonstandard posts limit your choices to replace it cheaply.

4) It is hidden in the back of the car, so it is important to know there are charging posts under the hood.

 

That's about it. If everything is normal after the correct battery is in place then all is well. If they installed the wrong battery with reversed polarity then it may have done up to a few thousands in damage. Various system settings will be lost in any case (radio presets, fuel economy display, etc.)

Don't return to that dealer. He's an idiot. There is no direct replacement for the Prius 12V battery.

 

I dearly hope that it was towed on a flatbed or with the front wheels on a dolly? Trying to tow a Prius with all wheels on the road at speed (that is, other than dragging one a few feet up and onto a flatbed) can destroy the transmission.