12V Battery

[JohnD2]

Hi. I've noticed a number of recent posts regarding problems likely to be caused by the 12v Battery: I suppose it's that time of the year. FWIW I offer the following. A couple of months ago, I was experiencing an occasional need to press 'Start' twice, accompanied by the big red triangle and various combinations of alarm lights. I checked the 12v and it was down to 10v. I removed the Battery to a workbench. Underneath the thin plastic 'advice' tape on the top there is a clear plastic lid covering the cell vents. I found that the four centre cells had no electrolyte visible. I added well over a pint of Battery (and smoothing iron) top-up water: enough to cover the plates/separators by about a 1/4 inch. Within a week, the symptoms had ceased and (crossed fingers) it seems ok now. I realise that not everyone will want to do this but we are living in an age where the 'throwaway' attitudes are going to have to change. H T H someone.

[MLW2233]

I thought these were gell batteries. I agree, if it works, great, but I fear you may only have a few weeks as empty cells degrade the Battery. Europarts have a 15% discount on batteries at the moment. Some top brands and good prices

[JohnD2]

Only time will tell, but its looking promising. And it was definitely liquid in cells 1 and 6.

[cuius]

Wow - that takes you back - must be at least 20 years since I've topped up a Battery - didn't realise they still made non-sealed batteries

[korat102]

Interesting. Gel batteries aren't supposed to lose electrolyte through evaporation. If the gel has been damaged, that could point to overcharging. I'd be surprised if your fix lasted very long to be honest. Unless, of course, it's not an original gel Battery...

Must admit, I didn't check mine when I changed it. Didn't even occur to me to try and top it up...

[inspiredron]

Four cells took a huge amount of water - I AM NOT SURPRISED! Please check out my post which relates to the Series 3 - http://www.toyotaownersclub.com/forums/index.php?showtopic=141460

My Battery is being charged at 14.6V most of the time and consequently is having its electrolyte "boiled off" - well not boiled but converted by electrolysis of the water in the dilute sulphuric acid into hydrogen and oxygen gases which are then vented away (otherwise the Battery would explode!).

AND YET TOYOTA UK TELL ME THAT THIS IS WITHIN SPECIFICATION! (Yes I am shouting!). Can that really be right?

I suspect that the same had happened to your Battery, hence the need for an enormous top-up.

I am interested that you were able to top up yours and will try with mine - I had thought they were sealed.

I agree that they are definitely not gel batteries.

Sadly, the only responses to my topic have suggested that I buy a different type of battery - which will probably also be ruined by Toyota's specification.

[timberwolf]

According to my SG2 my Gen 2 Prius is only charging at a maximum of 13.8V although I've never bothered to check with a DVM at the voltage being supplied to the 12V Battery terminals.

I love this myth about the Prius having a Gel type Battery, when I took my 12V Battery out it definitely had a sloshing sound and sounded just like any other regular lead acid car battery.

[inspiredron]

According to my SG2 my Gen 2 Prius is only charging at a maximum of 13.8V although I've never bothered to check with a DVM at the voltage being supplied to the 12V battery terminals.

I love this myth about the Prius having a Gel type battery, when I took my 12V battery out it definitely had a sloshing sound and sounded just like any other regular lead acid car battery.

My friend's Series 2 also charges consistently at under 14V. I have found a similar thread on Priuschat, here,

http://priuschat.com/threads/12-battery-maintenance.111532/

so I am not alone in suffering from overcharging on the Series 3. I guess that it will be unusual on the Series 2. I'd never have found the cause without the SG2.

[timberwolf]

Your hypothesis is unproven, and just jumping on every thread with a failed 12V Battery and claiming it is due to over-charging doesn't prove anything.

I would guess due to a lack of posted messages on the subject, that most Prius Gen 3 owners do not have an early death of their 12V batteries.

The most likely cause of an early failure of the 12V Battery is low annual mileage, infrequent usage, or bad habits (such as listen to the radio with the engine switched off) - can you demonstrate that you have ruled out these possible causes?

[inspiredron]

Your hypothesis is unproven, and just jumping on every thread with a failed 12V battery and claiming it is due to over-charging doesn't prove anything.

I would guess due to a lack of posted messages on the subject, that most Prius Gen 3 owners do not have an early death of their 12V batteries.

The most likely cause of an early failure of the 12V battery is low annual mileage, infrequent usage, or bad habits (such as listen to the radio with the engine switched off) - can you demonstrate that you have ruled out these possible causes?

Timberwolf

My annual mileage is around 6000 to 7000, as it has been in a variety of cars for the last 47 years. I do NOT listen to the radio with the engine off, nor have I ever, on this car, left interior lights or any other Battery draining devices on. To my knowledge I have no bad habits that would result in Battery drain.

While I accept that my hypothesis is unproven, in general terms, I believe that i have made an intelligent deduction from the information that has been made available to me viz:

1: My Prius charges the 12V Battery at 14.6V when the lights are on (actually it is now charging at 14.6V (SG) full time and the voltage measured with my digital voltmeter at the battery terminals is 14.8V!)

2: Toyota technical experts via their UK customer services dept tell me that charging at 14.6V when there is any load is "within specification" which I interpreted as "intended".

3: Numerous sources on the web reinforce my own knowledge garnered over my 54 years of driving (including around 40 years of maintaining my own vehicles) that maintained charging at voltages much above 14V will result in gassing of the electrolyte (electrolysis of the water content of the electrolyte). See http://en.wikipedia....omotive_battery for a particularly good summary, particularly the section headed "Exploding batteries".

4: If a battery is sealed then the electrolyte lost through gassing cannot be replaced.

5: If the electrolyte level falls then the battery will cease to work as required.

Hence the title of my other post "Excessive charging voltage kills 12V battery on Prius 3?" and please note the question mark!

In my correspondence with both Jemca Croydon and with Toyota Customer Services I have expressed surprise that many more Series 3 owners are not complaining about this issue. My motive in starting the other thread was to see if it stimulated others to express similar concerns, which, as you say, it has failed to do. Maybe nobody is monitoring charging voltage, particularly as it is not easy to do without a SG2.

When first analysing my problem I was ready to believe that my relatively low mileage would lead to a higher proportion of charging time being at the initial 14.6V level which is quite normal and that this could possibly result in shorter battery life - but that argument carried much less conviction once I saw that the 14.6V was maintained indefinitely with lights on, ie for any night journey.

In the light of Toyota's assertion that 14.6V is normal I would welcome it if you would give me an alternative hypothesis that could explain my problem. The only alternative that I can see is that there is actually a fault in the charging system on my particular vehicle and that Toyota told me lies (or perhaps less than the full truth) before my warranty expired in the hope that I will go away. I am somewhat reluctant to accept that as a credible alternative hypothesis.

Finally, I am not "jumping onto any thread" that supports my hypothesis in order to prove it. As a qualified actuary I understand the absurdity of that! I am merely attempting to introduce some helpful cross referencing which I don't think can be done in any other way apart from putting links in the relevant separate threads. It is interesting, however, that both threads that I have "jumped on" were vehicles with batteries where the electrolyte was half empty.

I hope that I have adequately explained my motives!

Ron

[kithmo]

I've had my Gen 3 from new since May 2010. I do around 6k miles a year, 70% short commute 3 miles to work, currently on just over 16k and 2yrs 7 months old. I would think that my usage would be very detrimental to the 12v Battery but I've had no problems whatsoever (touch wood).

After reading this post, I checked the Battery voltage using the Nav in diagnostics mode and ignition in accessory mode and the votage was 11.5V. In ready mode it went up to 14.1V with no load and stayed on 14.1V with the headlights, full blower and rear screen demister on.

At the Battery terminals with everything switched off the voltage is 12.4V.

I can only assume from this Ron, because my car is slightly newer than yours, that either (1) I have problems yet to come or (2) there is something wrong with yours.

Try the Nav diagnostic mode, hold "INFO-TEL" button whilst turning the headlights on and off 3 times, select "Function check/setting" then "Vehicle signal" and see if your is the same as mine.

Searching the internet I came across two different schools of thought for safe/sufficient charging voltages (although this was to do with alternators rather than as in the prius), one said 13.8 to 14.2V, the other said 13.8 to 14.8V. Only one of them mentioned boiling off the electrolyte and that was if the voltage was above 15V.

Edit: Found another site that mentioned Lead Acid battery will boil if charge voltage is over 14.34v.

[inspiredron]

Keith,

Thank you so much for your helpful post. I did not know about the Nav diagnostic mode so have just tried it. I could not get it to go into diagnostic unless I was in running mode but then it showed 14.2V while the SG2 showed 14.6V. I did not check voltage at Battery terminals but would guess that it was 14.8 as noted in my previous post. If I had changed to accessory mode while in diagnostics would the diagnostics screen have stuck? Oh, and by the way I dropped back to Function check and then then back to Vehicle signal in case the voltage does not update regularly. There was no change which could mean that to update readings you have to drop right out.

Your 14.1V and my 14.2 are not different enough to be significant - and both are actually measuring inverter low tension voltage. But that short test is not terribly helpful because at startup the charging voltage WILL be around 14 to 14.5 for the first few minutes - that is quite normal. Mine used to be there for the first 1 or 2 miles and then dropped back to an acceptable 13.5 or thereabouts - unless I switched on lights when it would not fall back.

I hope that you don't have problems to come. 12.4V at Battery terminals under no load is OK (it means about half charged) but if that drops to 11.5V under load then I suggest that indicates that the Battery is starting to fail. When my first battery failed at 2 years it was down to around 10V. A good battery should be within around 12.2V to 12.8V under a reasonable load - say 5 amps. With 10 amps (dipped headlights) I would expect a drop to around 12.5V at the high end but the low end should not, in my opinion, drop below 12V. ( I stand to be corrected on this!)

As far as safe charging voltages are concerned, they do vary a bit between wet and gel batteries. We all agree that the Prius battery is a wet one, albeit of the sealed variety. Gel batteries can take the higher voltage for longer before damage occurs. The German made mains charger on my previous motorhome had two settings, one for gel and one for wet batteries. The essential difference was that the wet setting provided around 14.4V for 1 hour and then dropped to 13.5, on the gel setting the time at the higher voltage was extended from 1 hour to to 3 hours. That charger pre-dated the intelligent CTEK type mains chargers often used nowadays. But it does not matter whether the charging is from an alternator, the mains or Prius inverter - what concerns the battery is the charging current and voltage which are inter-related.

Thanks again

Ron

PS Your usage is very close to mine both in daily and annual mileage.

[kithmo]

I could not get it to go into diagnostic unless I was in running mode but then it showed 14.2V while the SG2 showed 14.6V. I did not check voltage at battery terminals but would guess that it was 14.8 as noted in my previous post. If I had changed to accessory mode while in diagnostics would the diagnostics screen have stuck? Oh, and by the way I dropped back to Function check and then then back to Vehicle signal in case the voltage does not update regularly. There was no change which could mean that to update readings you have to drop right out.

The diagnostic mode readings are live on mine. What I did was, foot off brake, press power button (acc mode, no dash display), wait for nav screen to boot up, press and hold "INFO-TEL" button, turn headlights on then off three times, bringing up the diagnostics screen in acc mode. Selected function check, vehicle signal and it read 11.3V this morning after standing overnight. Pressed brake pedal, the voltage dropped to 10.8V whilst the brake pressure pump ran then went back up to 11.3V when it stopped. I pressed the power button again to go to ready mode (dash lights on), the diagnostic screen stayed on and the voltage went up to 14.1V.

There is no way to drop back to acc mode from ready mode (AFAIK) without turning it off.

As a matter of interest, SWMBO has a Gen 2, which is over 6 years old on the original Battery, which has done only 4-5k miles a year on shorter journeys than me, several 0.5 miles and 0.25 mile journeys in the week and about 5-10 miles at the weekends. She only had a problem once when I left the interior light on all night but after a jump start and a 5 mile run she's had no more problems since.

Remember though that the 12v Battery is not a starter Battery as on a normal car and it only needs enough power to boot up the car systems and to energise the relay to connect the HV battery, so the battery going low is not going to be a problem, unless you don't use the car for a long time, in which case it would be too low to energise the HV battery.

I think the car needs to be used everyday or th 12V battery trickle charged if left for several days to keep it topped up.

I agree with your point about damaging the battery if it's overcharging because IMO it is a weak battery anyway.

[timberwolf]

As far as I am aware, all three Prius generations available internationally have had complaints about short life times for the 12V Battery when the Prius is used less.

The apparent low levels of electrolyte have been noted in Gen 2 batteries where the charging voltages are lower than the Gen 3 - so either the low level is normal, or the loss of electrolyte is not mainly caused by boiling at the electrodes (unless you believe 13.8V is too high also?) and the subsequent need to the vent the gas due to pressure. Maybe a "sealed" Battery isn't that well sealed?

It is not certain whether the electrolyte is supposed to cover the plates in the 12V Battery, that could be an erroneous assumption. There is a warning label on the battery not to top it up, and something about explosions, maybe the electrolyte level is low to prevent the battery from exploding!?

The UK Spec Gen 2 does not have SKS keyless entry so I'd expect it to have a lower standby current drain from the 12V battery than the Gen 3 - this is based on the observation from those in the USA that the Gen 2 came with different sized 12V batteries depending on whether they had SKS or the regular key fob. I'd also expect the UK Gen 3 to have a higher capacity 12V battery (in Ah) than the Gen 2 although the external packaging of the battery may be the same size.

I don't understand why the charging voltage would be higher at the 12V battery terminals - shouldn't there be a small voltage drop from where the voltage is produced at the front of the car (DC-DC converter) to where it is being used to charge the 12V battery at the back of the car?

Based on the experience of many Generations of Prius, I would say your primary problem is still about lower usage and the higher standby current demands of the Gen 3 to power its extra toys when the car is a sleep.

[inspiredron]

Keith:

I got into Diagnostics this morning without any problem in Accessory position - must have been tired last night! I had 11.2V which dropped to 10.8 when I put headlights on and then partially recovered to 10.9V after a few moments. I then left the screen on during a 4 mile drive. It does update everything on a live basis but the voltage stayed constant at 14.2V. Speed in kph was, as expected, around 12% lower than the speedometer which as we know is absurdly optimistic by design. My friend with a 57 reg Series 2 has had no Battery problems either, but his journeys tend to be longer. Can you try leaving the screen on diagnostic while driving and see whether the voltage drops to around 13.5 or so after a mile or two. If it does, then does it go up again and stay up if you put the headlights on?

Timberwolf:

I don't know whether the S2 and S3 batteries are different capacities - they do look the same. "Sealed" refers only to the ability to top up. A sealed Battery has no cell caps to unscrew, though it appears that if you take off all the warning labels that you can remove a snap on cap, and presumably snap it back on. If you look carefully at your Battery you should see a black vent tube coming from the front end and disappearing through the floor. That is the safety which allows the hydrogen and oxygen to be safely vented - and there is no valve which holds them back. If the vent was not there then the battery would explode with dire consequences. Electrolyte level should be such as to JUST cover the plates, no more and no less - more gives the chance to spill electrolyte from the vent tube and less reduces the electrical capacity. The different voltages that I have measured with the different instruments could be errors in calibration, particularly my voltmeter which is fairly cheap but the SG2 I would expect to be pretty close tolerance. Why the diagnostic screen only shows 14.2 mystifies me in the context of the 14.6V from SG which was consistent with the readings taken by Jemca on their test equipment. No - there should be only a minimal voltage drop between inverter and battery as the leads should be heavy duty - and are.

I don't have any quarrel with a 13.8V charging voltage, but remember that the voltage even on a S2 is up at around 14.6 for the first mile or two. If a S2 owner does really low mileages and does not use a mains charger at all then they may have a large part of charging at excessive voltage which might just cause deterioration, though short periods should not matter. Also, the problem of returning from holiday to find a flat battery, which was prevalent on S2 has been "fixed" on the S3 - maybe by the excessive charge rate as well as by going into a deep sleep after a day or two without use? Please also remember that my concern did not escalate until I saw 14.6V charging full time when lights are on. That does not happen on the S2, at least not according to my friend. Sorry, I cannot agree with your last sentence - but I guess that we need to agree to differ on that.

[timberwolf]

I assume your short hand S2 and S3 refer to Gen 2 and Gen 3 although reading through your block of text I wasn't always sure that you had not meant S3 instead of S2 in some places?

I have never seen the charging voltage go above 13.8V on my Gen 2, first mile or otherwise. The charging voltage range I've seen varies from 13.5V to 13.8V.

Whether a Gen 2 or Gen 3 survives a holiday is entirely dependent on the health and SoC of the 12V Battery.

The 12V Battery on my Gen 2 survived 4 weeks (probably closer to 5 weeks) at this time year (it was colder) whilst I was being treated in Southampton General Hospital two years ago (I missed both Xmas and New Year that and then later on Easter), the car was two years old at the time. It is now 4 years old and the 12V Battery was only just replaced last month. I think my car coped quite well with its "holiday" even if I have had to help it with the occasional session of charging.

The ScanGauge2 tool is a CANBus reader, it only reads digital packets of data from one of the car's data networks. The voltage displayed on the SG2 comes from packets of data, and the voltage is measured by one of Toyota's sensors built into the Prius and not from the SG2 tool itself. I doubt anyone outside Toyota or their suppliers knows the accuracy or tolerances of the voltage sensor(s)?

[inspiredron]

I assume your short hand S2 and S3 refer to Gen 2 and Gen 3 although reading through your block of text I wasn't always sure that you had not meant S3 instead of S2 in some places?

I have never seen the charging voltage go above 13.8V on my Gen 2, first mile or otherwise. The charging voltage range I've seen varies from 13.5V to 13.8V.

Whether a Gen 2 or Gen 3 survives a holiday is entirely dependent on the health and SoC of the 12V battery.

The 12V battery on my Gen 2 survived 4 weeks (probably closer to 5 weeks) at this time year (it was colder) whilst I was being treated in Southampton General Hospital two years ago (I missed both Xmas and New Year that and then later on Easter), the car was two years old at the time. It is now 4 years old and the 12V battery was only just replaced last month. I think my car coped quite well with its "holiday" even if I have had to help it with the occasional session of charging.

The ScanGauge2 tool is a CANBus reader, it only reads digital packets of data from one of the car's data networks. The voltage displayed on the SG2 comes from packets of data, and the voltage is measured by one of Toyota's sensors built into the Prius and not from the SG2 tool itself. I doubt anyone outside Toyota or their suppliers knows the accuracy or tolerances of the voltage sensor(s)?

I have reread my post. As you say S2 and S3 were shorthand for Series 2 and Series 3 (More properly Gen 2 and Gen 3 if you wish) but my references were not muddled.

My 12V Battery has survived 4 week absences as well but, in retrospect, I should probably have given it a charge afterwards

My quote about the Generation 2 starting to charge at around 14.5V was based on my friends experience with his 57 Registration Generation 2 vehicle.

You are absolutely correct that the SG2 gets its information from the CANBUS but the display discrepancy between SG2 and Prius Diagnostic Screen may be due to them using different multipliers as they will interrogate the same sensor. Given that the SG2 seemed to agree with Jemca's diagnostic equipment it could be that the Diagnostic Screen is wrong, just like the speedometer! Does your diagnostic screen agree with your SG2?

[timberwolf]

My quote about the Generation 2 starting to charge at around 14.5V was based on my friends experience with his 57 Registration Generation 2 vehicle.

Ah, that's the one I was thinking about. Interesting the possible variation between two different cars of the same generation although manufactured in different years? The other possibility is that your friend miss-read the voltage displayed and it was reporting 13.5V?

You are absolutely correct that the SG2 gets its information from the CANBUS but the display discrepancy between SG2 and Prius Diagnostic Screen may be due to them using different multipliers as they will interrogate the same sensor. Given that the SG2 seemed to agree with Jemca's diagnostic equipment it could be that the Diagnostic Screen is wrong, just like the speedometer! Does your diagnostic screen agree with your SG2?

Sorry, I forgot the method that I used to use to switch to the Diagnostic mode, and because it was dark I didn't want to do the switch the lights on and off ritual.

My charging voltage displayed on the SG2 dropped to 13.5V last night, new Battery I guess, and I had the headlights on but I didn't notice at what point in the journey the voltage dropped from 13.8V.

[kithmo]

Ron, I drove to work, 3 miles, yesterday with the diagnostic screen on and lights and heater on and the voltage stayed at 14.1 all the way. I'll try it with the lights off next bright day we have.

[JohnD2]

Update:- currently (excuse the pun) still going strong. My S2 annual mileage is c 5 to 6 k; and often only used twice a week. J

[JohnD2]

Hi. I regret having to inform readers that the experiment has failed. I have had to replace the Battery. Tid-bits of info gleaned over the three months of extended life: there is a permanent drain of 20 mA (20 thousandths of 1 amp) on the T-spirit. The smallest (350?mm diagonal) Maplin solar panel will provide roughly 100 mA into a partly charged Battery in strong sunshine; but during an overcast November day it's down to around 5 to 8 mA. My car system charges the 12v Battery at 14.2v.

[timberwolf]

Thanks for the update. Personally, I went for the £90 Battery replacement, it is easier, but not as much fun!?

I find what may be a possible difference between your and my car's charging voltage curious, mine is measured by the car (and read with a ScanGauge 2) or from the jump start point and it has varied between 13.5V to 13.8V (it is usually at the higher voltage because I don't drive much).

[JohnD2]

Hi T W. 1. I was quoted (Toyota Sandurst), £95; but then given a discount? which brought it down to £80. The storeman there is an unsung hero and even carried it to my car. How times have changed. I'd be very interested in anyone else's experience of buying/using a cheaper copy. 2. Re, difference in charging voltage. Is it possible that this could be due to tolerances in component manufacture? eg voltage stabilising diodes etc. 3. I haven't yet been successful in using the built-in (Camdata?) system. From info on the forum, I understand the procedure to be as follows:- key in, no footbrake, press power button once (what colour), wait for screen to show (what is screen heading), select 'Function Check', select 'Vehicle Signal, turn headlights on then off three times. When I press the power button it stays green, and the screen stays on whatever page it was on at last shutdown.

[timberwolf]

Hi T W. 1. I was quoted (Toyota Sandurst), £95; but then given a discount? which brought it down to £80. The storeman there is an unsung hero and even carried it to my car. How times have changed. I'd be very interested in anyone else's experience of buying/using a cheaper copy.

Snows parts man initially quoted a bit higher than the Fixed Price Repair Promise price of £90. When I pointed that out, he went way to check and said he would match the Fixed price promise but didn't volunteer anything lower. He did arrange for my car to be booked-in for the repair.

You'll see mention of the Bosch S4 155 Battery. As a temporary replacement, I also bought one of these for £46.87, but recent threads suggest that it has gone up in price! The Bosch Battery dimensions fit, but the vent port on side of the Battery is too small for Toyota's elbow adapter. ISTR one member filing their adapter down until it fitted. I had the fun and games of not having a socket extension long enough to undo the bolt between the 12V Battery and the black capacitor box (emergency brake power supply), the fun of dropping the bolt used to secure the HV Battery exhaust pipe and it landing underneath the 12V battery, meaning I had to dismantle it again and remove the battery.

As I wasn't getting any discount from Snows, I might as well use them to repair it, mechanic left an oily thumb print on the cargo roller blind, which did not impress me.

2. Re, difference in charging voltage. Is it possible that this could be due to tolerances in component manufacture? eg voltage stabilising diodes etc.

3. I haven't yet been successful in using the built-in (Camdata?) system. From info on the forum, I understand the procedure to be as follows:- key in, no footbrake, press power button once (what colour), wait for screen to show (what is screen heading), select 'Function Check', select 'Vehicle Signal, turn headlights on then off three times. When I press the power button it stays green, and the screen stays on whatever page it was on at last shutdown.

CAN Bus. http://en.wikipedia.org/wiki/CAN_bus

I used to use an alternate procedure because I never liked the head light switching on-off method. I now use the ScanGauge2 scan tool that plugs into the OBDII diagnostic socket.

http://priuschat.com/threads/entering-maintenance-mode-aka-12v-battery-check-without-switching-headlights-on-off.78412/

[JohnD2]

Thanks again T W. I think we've exhausted the topic of the 12 v Battery. My car is now definitely perkier and I will watch the mpg with interest. I'm still not having any success with the Priuschat procedure but I think that ought to go to a new thread.