Charging/maintaining the 12v battery

finally_got_one · 05-05-2006, 01:36 PM

Ok, I think that the topic of how the 'big battery' is charged has been gone over quite a bit. So how is it that the 12 volt battery is recharged? Is it in the same loop at the appropriate voltage? What needs to be done (if anything) to keep the 12 volt battery healthy?

On my old Accord (which I no longer have...), I had to 1) make sure the battery had water (an old lead/acid type), 2) clean the contacts with soda water every once in a while, 3) make sure that the battery could hold charge, and 4) replace the battery ever so often as it ran down. I have seen nothing that I need to do for the Prius 12 volt battery, which is fine with me. My Accord had an 'idiot light' for the battery. This light came on every time I started the car. So how do I determine the health of the battery on the Prius? Or, like the old lead-acid type, do I just drive until the 12 volt battery quits before replacing it?

eagle33199 · 05-05-2006, 03:11 PM

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.

tochatihu · 05-05-2006, 07:09 PM

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.

mrbigh · 05-06-2006, 12:21 PM

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

Quote:

Ok, I think that the topic of how the 'big battery' is charged has been gone over quite a bit. So how is it that the 12 volt battery is recharged? Is it in the same loop at the appropriate voltage? What needs to be done (if anything) to keep the 12 volt battery healthy?

On my old Accord (which I no longer have...), I had to 1) make sure the battery had water (an old lead/acid type), 2) clean the contacts with soda water every once in a while, 3) make sure that the battery could hold charge, and 4) replace the battery ever so often as it ran down. I have seen nothing that I need to do for the Prius 12 volt battery, which is fine with me. My Accord had an 'idiot light' for the battery. This light came on every time I started the car. So how do I determine the health of the battery on the Prius? Or, like the old lead-acid type, do I just drive until the 12 volt battery quits before replacing it?

[/b]

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.

c4 · 05-07-2006, 01:06 AM

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"..

tochatihu · 05-07-2006, 11:37 AM

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.

mrbigh · 05-07-2006, 06:21 PM

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

Quote:

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"..
[/b]

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.

jayman · 05-08-2006, 10:29 AM

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

Quote:

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. ... 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..
[/b]

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.

05-05-2006, 01:36 PM	#1
finally_got_one Join Date: Mar 2006 Location: Orange County, California Posts: 151 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Ok, I think that the topic of how the 'big battery' is charged has been gone over quite a bit. So how is it that the 12 volt battery is recharged? Is it in the same loop at the appropriate voltage? What needs to be done (if anything) to keep the 12 volt battery healthy? On my old Accord (which I no longer have...), I had to 1) make sure the battery had water (an old lead/acid type), 2) clean the contacts with soda water every once in a while, 3) make sure that the battery could hold charge, and 4) replace the battery ever so often as it ran down. I have seen nothing that I need to do for the Prius 12 volt battery, which is fine with me. My Accord had an 'idiot light' for the battery. This light came on every time I started the car. So how do I determine the health of the battery on the Prius? Or, like the old lead-acid type, do I just drive until the 12 volt battery quits before replacing it? __________________ 2006 Package #3 'Seaside Pearl'

05-05-2006, 07:09 PM	#3
tochatihu Senior Member Join Date: Apr 2004 Location: Kunming Yunnan China Posts: 1,823 My Car: 2001 Prius Package: Pioneer #1 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 7	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. __________________ DAS Tochatihu, the Hopi hummingbird kachina

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Continuous battery charging!	lafolet3	Prius Main Forum	5	02-05-2007 01:11 PM
Odd Battery Charging Behavior	bobh3501	Prius Modifications	3	12-27-2006 05:35 PM
Charging HV Battery to MFD full SOC	Presto	Prius Main Forum	10	08-29-2006 11:02 AM
Charging HV battery	whodat	Prius Modifications	4	07-22-2006 04:49 PM
RC car battery charging with the Prius	pafoss	Prius Main Forum	3	03-19-2006 03:07 PM

05-05-2006, 03:11 PM	#2
eagle33199 Platinum Member Join Date: Mar 2006 Location: Minnesota Posts: 3,648 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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.

05-07-2006, 01:06 AM	#5
c4 Join Date: Mar 2005 Posts: 523 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	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"..

05-07-2006, 11:37 AM	#6
tochatihu Senior Member Join Date: Apr 2004 Location: Kunming Yunnan China Posts: 1,823 My Car: 2001 Prius Package: Pioneer #1 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 7	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.