12 V battery Voltage

The charging voltage appears correct. The standing voltage would indicate no more than 40% charged. Please review the battery SOC articles I linked in the other thread

As I indicated in the other thread, if I check the standing voltage in my Prius, it's usually 12.9-13.1 vdc after resting 4 hours

If the dealer is unwilling to do anything about this, it appears you will have to remedy it yourself. Much better if you have a garage to work in, out of the weather.

Pop the rear hatch, remove the trim cover, and proceed to remove the diabolical red plastic cover over the pos terminal. Remove the neg cable clamp, then the pos cable clamp. Hold down is next, don't forget the vent tube either

Once the battery is out, hook it up to an automatic battery charger set for 10 amps. Don't be surprised if it needs 4-6 hours, even overnight. With an automatic charger, I'd just leave it overnight anyway

With the battery out, back off the negative cable bolt that is secured to the unit body, then snug it up again. I found mild corrosion on the bolt first time I checked it, so every Spring and Fall I back the bolt out and snug it up again to break the corrosion. This will give a better connection

After the battery is put back in, expect the alarm to go off, so have the fob handy to cancel it. My alarm has gone off every time I have removed my 12 vdc battery.

You will also have to put the presets back into the radio and "normalize" the power windows. If I recall, that means holding the button all the way down for about 5 secs after the window is down, then power the window up again. Continue to hold the window button in the up position for 5 secs. This is to set the anti-pinch if I recall

If the battery continues to act up - go dead - then you will need a good ammeter to check for excessive parasitic current draw. Anything over 35 mA should be looked into

Some early build Prius second generation (2004-2005) had a defect in the JBL amp that caused excessive standby parasitic draw.

 

Frosh,

Your Prius charges the 12v battery by supplying just under 14 volts via a DC-DC converter whenever you are in "ready" mode. This is a very slow way to charge that battery (to avoid overcharging with simple electronics). A "Battery Minder" could be used in your garage overnight to get it more fully charged, or you could go on a long road trip .

Jeff

 

Why would you have to remove the battery to charge it with a standard 10 Amp automatic battery charger? Couldn't you just connect it to the jumper cable posts in the engine compartment?

I would think this way, you wouldn't loose any presets etc...

 

There have been a number of posts like yours on here. If I recall correctly, the most common causes of 12v battery running down (besides a bad battery) is leaving the key fob too close to the car, or leaving an inside light on, or door or trunk ajar (thus the light stays on). Some people always lock the car so they know all doors are closed. Hope you figure it out!

btw, scangauge reports 13.7 running, 12.5 a minute after shutting off.

 

Frosh,

My accessory battery readings (using the MFD) are 13.8 volts in ready mode and 12.4 volts in accessory mode. I have never had battery problems in 4 years (2004 Prius) and 106,500 miles of use.

JeffD

 

Now I'm wondering if the dealer even bothered to properly charge the "new" battery, or just put it in as-is? A battery that has been sitting in a warehouse for 6-12 months will usually have less than 40% charge. The voltage readings you have posted would indicate 40% or less charge

With conventional cars, a "mechanic" will just take the battery off the shelf, hook it up to the car, and let the alternator cook itself trying to charge the "new" battery.

Any battery I have replaced myself, I properly charge up first. Now with my VDC Battery Minder units always plugged into equipment I'm not using, I no longer have to replace batteries every 2-3 years.

Given the issues you're having, in the long run it would be easier to just take out the 12 vdc battery and fully charge it yourself. Be prepared to bugger up that diabolical red plastic cover over the pos post

 

I think it's ok to leave something like a VDC Battery Minder hooked up all the time. I've been doing so for +3 years with no ill effects.

However, the official Prius PDI (Pre Delivery Inspection) is pretty emphatic on the need to remove the battery first. Though I suppose just leaving a battery charger hooked up to the jump start posts shouldn't harm anything

 

I think Toyota are worried about damage to the electronics in the car from certain "battery chargers". A friend was purchasing one, and gave me four different models to test. I used a scope as well as a load and battery to test them. Some put out pulses as high as 50V when turned on. This -could- damage electronics.

A "battery tender" would be safe, based on my measurements. I suspect the battery minder is also safe. Beware the cheep "battery chargers" you can buy for less than $40. Some are just fine, some are dangerous when the battery is connected to the car.

Of course, you could just disconnect the -ve post and then charge in the car. That would be safer and easier than removing the battery. If there's a problem with the charger though, the car could be contaminated with battery residue (if it bursts or explodes).

 

I agree. Since there are so many chargers out there, of all ages and quality, they can't make a blanket recommendation except to tell you to remove the battery first

Of course, just disconnecting and removing the battery is risky. Drop a wrench just right and ZAP BOOM

 

12 Volt (12v) Toyota Prius Auxilary Battery for 2004, 2005, 2006, 2007 and 2008

Upgrade!

 

How about a battery conditioner? I plan to just plug it in through the 12V outlet from inside the car. Is this ok?

 

Pretty sure this is a no go, Prius disconnects aux outlets from battery when power is off.

FYI, '05 owners manual states the following:

Open Voltage at 20C (68F):
12.6-12.8V Fully Charged
12.2-12.4V Half Charged
11.5-11.9V Discharged

Rob

 

This manual on Yuasa AGM Motorcycle batteries has a pretty good section starting on page 24. Some of the details will be slightly different, but the basic idea should be similar for the Prius battery. Voltages are pretty similar to owners manual, they say under 12.5V (75%) open resting voltage should be charged.

http://www.yuasabatteries.com/pdfs/TechMan.pdf

Anyone noted the actual manufacturer, part number or capacity of the Prius OEM batteries? It would be interesting to see if an actual datasheet could be found for it.

Rob

 

I just want to submit some alternate data about battery voltages and SOC determinations. I have been using and recycling lead acid batteries for campers and racecars for a long time. I read the mpower article about determining state of charge from voltage but I think there is a quite a range of ambiguity in their data. For example, by their chart, a battery that reads 12.8 volts can be anywhere from 60% to 100% of full charge at 25 deg C. Obviously, you can't really know for sure. In fact, my experience is that most new deep cycle batteries will initially read as high as 13.5 volts open circuit immediately after charging and then drift down to 12.8 or so volts within 2 - 3 hours after charging. In other words, I rarely see a resting full charged battery higher than 12.8 volts. In my testing the roughly 50% point is usually more like 12.0 volts.

So, I guess my point is, without trying to argue chemistry and specific gravity and such, is that we shouldn't necessarily be telling people that a 12.4 volt battery is only 40% charged. I'd rather say that you can't really know for sure unless you charge the battery and make an educated guess based on how much charge it seems to take.

In fact, as I read a number of these recent posts, I'm not sure I'm really hearing that these batteries are dead. Some may be, but others may be secondary problems that we're jumping to conclusions are due to dead batteries. So, I'm not trying to start any trouble, just proposing that we need to look carefully at these reports and make sure we're not overlooking something else.

Steve

 

I agree there is a large range and the actual voltage read can be influenced by surface charge and temp. According to the Toyota PDI, this is how to determine if the 12 vdc battery needs charging:

If after charging or driving, put the headlights on for 60 secs. Wait 60 secs. Use a DMM to measure voltage directly at the battery. If the reading is 12.8 vdc or less, the battery needs charging

I suppose waiting 24 hours will also allow the surface charge to dissapate, then a reading can be taken. Using the Battery Minder on my batteries, a 24 hour rest will result in battery voltages of 12.90-13.19 vdc

 

That is the catch to any problem where the car will not boot. Unfortunately, the car cigarette lighter is only "live" once booted or possibly in Acc mode. If you cannot get into that mode due to a low battery, the cig lighter plug will not work

Oddly enough, my FJ cig lighter plug is also dead when the motor is off and the key is removed from the ignition

There is a mod to allow the cig lighter plug to always be "live." That may help in this situation