12 V battery Voltage

frosh · 01-23-2008, 10:46 AM

Hi all,

I have had a couple of times where the 12V battery ran empty after my Prius was sitting in the garage for a day or two. The dealer never found a a reason.
Could you please post Voltmeter readings here for comparison. My Prius consistently reads these voltages:

standstill - charging
12.45 - 13.91

thanks, frosh

jayman · 01-23-2008, 11:02 AM

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 · 01-23-2008, 11:13 AM

Thank you jayman, you've been providing high quality information. I will do the battery test, but still I am kind of suspicious, if my battery ever gets charged fully. Dealer already replaced the battery, so it doesn't look like the battery is bad. The other thread went kind of hybrid, so I just wanted to start a new - focused - thread.

appreciate,
frosh

jdenenberg · 01-23-2008, 12:54 PM

Quote:

Originally Posted by frosh

Thank you jayman, you've been providing high quality information. I will do the battery test, but still I am kind of suspicious, if my battery ever gets charged fully. Dealer already replaced the battery, so it doesn't look like the battery is bad. The other thread went kind of hybrid, so I just wanted to start a new - focused - thread.

appreciate,
frosh

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

PRIUS007 · 01-23-2008, 06:33 PM

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...

frosh · 01-23-2008, 07:06 PM

Sorry guys, this doesn't go where I want it ...
Could you please just post your voltmeter readings?
Yes, I am so stubborn but the more I'm curious about more readings.
Thanks,
frosh

abq sfr · 01-23-2008, 08:23 PM

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.

jdenenberg · 01-24-2008, 10:21 AM

Quote:

Originally Posted by frosh

Sorry guys, this doesn't go where I want it ...
Could you please just post your voltmeter readings?
Yes, I am so stubborn but the more I'm curious about more readings.
Thanks,
frosh

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

jayman · 01-24-2008, 10:45 AM

Quote:

Originally Posted by frosh

Dealer already replaced the battery, so it doesn't look like the battery is bad.

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

jayman · 01-24-2008, 10:47 AM

Quote:

Originally Posted by PRIUS007

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 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

01-23-2008, 10:46 AM	#1
frosh Member Join Date: Jan 2008 Location: Virginia Posts: 33 My Car: 2007 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	12 V battery Voltage Hi all, I have had a couple of times where the 12V battery ran empty after my Prius was sitting in the garage for a day or two. The dealer never found a a reason. Could you please post Voltmeter readings here for comparison. My Prius consistently reads these voltages: standstill - charging 12.45 - 13.91 thanks, frosh

01-23-2008, 11:02 AM	#2
jayman Senior Member Join Date: Oct 2004 Location: Winnipeg Manitoba Posts: 6,221 My Car: 2004 Prius Package: B Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 4	Re: 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. __________________ 2004 Toyota Prius "B", Tideland Pearl 2007 Toyota FJ Cruiser 5AT "C", Sun Fusion

01-23-2008, 11:13 AM	#3
frosh Member Join Date: Jan 2008 Location: Virginia Posts: 33 My Car: 2007 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Re: 12 V battery Voltage Thank you jayman, you've been providing high quality information. I will do the battery test, but still I am kind of suspicious, if my battery ever gets charged fully. Dealer already replaced the battery, so it doesn't look like the battery is bad. The other thread went kind of hybrid, so I just wanted to start a new - focused - thread. appreciate, frosh

01-23-2008, 06:33 PM	#5
PRIUS007 James Bond -007 Join Date: Jan 2008 Location: Mundelein, Illinois Posts: 75 My Car: 2008 Prius Package: #6 Touring Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Re: 12 V battery Voltage 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...

01-23-2008, 07:06 PM	#6
frosh Member Join Date: Jan 2008 Location: Virginia Posts: 33 My Car: 2007 Prius Package: #6 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Re: 12 V battery Voltage Sorry guys, this doesn't go where I want it ... Could you please just post your voltmeter readings? Yes, I am so stubborn but the more I'm curious about more readings. Thanks, frosh

01-23-2008, 08:23 PM	#7
abq sfr Senior Member Join Date: Mar 2007 Location: Albuquerque, NM Posts: 613 My Car: 2007 Prius Package: #2 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 1	Re: 12 V battery Voltage 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. Last edited by abq sfr; 01-23-2008 at 08:36 PM.