Toyota Yaris Mark 4: Voltmeter readings for 12V battery 

I have just had my 12V battery replaced under warranty because my car failed to start when it was only 10 months with about 6,200miles on the clock after just one day without use. My dealer has been very helpful and told me that the new battery was the "same spec" as the original factory fitted battery. However, I now realise that he did not say the new battery was from the same manufacturer as the factory fitted battery. Do you know the manufacturer of the new 12V batteries that will replace the bad Turkish batteries? I will then lift my rear seat and check if I have got a battery from the new supplier or the old Turkish supplier.

@@Helpful-Stuff I don’t know. Spec is probably the same. Issue is with actual brand which doesn’t perform properly, so Toyota changed it. It also depends when you had it replaced. Things just started processing, Toyota is introducing new testing procedure using new equipment. Apparently good question to ask is - “has my battery been tested according to new procedure?” Since they replaced it ( before they weren’t doing it) I assume you have new battery which should be fine.

My battery was changed 4 days ago ... so from what you are saying I think there is a very good chance that I have got a new 12V battery from the good manufacturer. Good news 😀 Thanks for the comment ... it is very useful information. Is it OK to make a video where I use the information that you have shared so that more people get to know about this? I guess from your anonymous RU-vid account name you would prefer to not be quoted directly so I will just say something like "I have discovered that ...."

@@Helpful-Stuff Yes. It’s public info shared by Toyota insider. You just have to speak Polish, but you can use Google translate. I would have to find it though as I stamp on it accidentally.

I have tried to find it using Google's advanced search to only search websites in Polish ...unfortunately no luck so far. If you do find it again I would very grateful if you can paste the link into this discussion. Thanks again for the information. 👍

Thanks for your comment and age/mileage information. My car is a couple of months older but has done a lot more miles ... I have just done 10,000miles. Its interesting that you are seeing 12.7V for the instantaneous reading immediately after starting the car. The highest I have seen in my car is 12.2V and that is on the 2nd or 3rd start of the day. It looks like the CTEK charger is a better battery charger than the 12V battery charging system built into the Yaris. Or another possibility is that my 12V battery was damaged by the single failure to start that I have experienced. I think this confirms that the voltmeter was a good purchase and I need to keep an eye on the voltages. I know what the normal voltages for my car are now ... if I start to see the voltages dropping then I think I will have to buy a new 12V battery. I have an allocated off road car parking space but unfortunately there isn't a 240V mains socket anywhere near it so I do not have the option of using a CTEK charger. Hence the reason I do the once a week wash + charge in READY mode.

My dealer has been extremely helpful during my "12V battery problem". They recommended the AA solar panel and they even fitted the cable free of charge so that it is a LOT easier to plug and unplug the solar panel ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-o8MkFUPfdvQ.html .... before the cable was fitted I had to get down on my knees to plug the solar panel's cable into the OBD socket below the steering wheel!!! It only took my dealer 10minutes to install the cable - they told me that only 2 screws need to be undone. If you are good at DIY then you may be able to do this yourself ... or if not then it may be worth asking your dealer ... from what I read some dealers are helpful and others are not so helpful. I am lucky I have got a very helpful dealer. I owned a Yaris Mark 3 Hybrid for 5 years and had no starting problems even during COVID lockdowns when I only used the car once per week. My Yaris Mark 4 failed to start after a single day parked ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE--UkrUwpkePM.html The small 12V battery problem is an issue for all manufacturers so I have looked at how other car manufacturers are handling the problem ... Kia and Hyundai Hybrids have a 12V Reset which prevents the 12V battery from being drained. MG EVs show the 12V battery voltage in the app. Toyota do not have a voltmeter on the dash or in the app and nothing like the 12V Reset button. My own view is that Toyota made a major mistake with the 12V design but they will not admit it because the cost of fixing the problem in every Yaris that has been sold is too high. So instead they are blaming customers for not driving enough!!!! I think this strategy will backfire in a big way on Toyota ... Toyota used to have a reputation for building reliable cars. The design flaw in the Yaris and the corporate arrogance in deciding to blame customers will be Toyota's downfall ... I think they will lose the reliability reputation as a result and will be paying for this for years in terms of lower sales. Like you I would not buy another Toyota ... even though my current car is my 3rd Toyota ... 2005 to 2018 Landcruiser ... 2018-2022 Yaris Mark 3 ... 2022 to date Yaris Mark 4

I have got a 2022 Yaris with the Tech pack which includes the head up display and Smart Connect Multimedia system (which from Googling I think is the TAS600 system that you mentioned). The only non-factory fit kit I have got is a voltmeter plugged into the accessory socket ... more info about the voltages I am seeing in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-0nYdnNVgvJI.html My car failed after a single day without use and does UK average mileage. My dealer's original position was that I am not doing enough mileage - which I believe is Toyota GBs standard position when talking to customers with a car that failed to start. I believe I do sufficient mileage to keep my 12V battery charged ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ctXDnI9uuYI.html The factory fit 12V battery is rated at 35Ah. I parked my car about 3pm on Tue 24-Oct and then tried to start it at 9am on Thu 26-Oct which means it was parked for about 42hours. So for a 35Ah battery to be drained there must be a parasitic current draw of 35 / 42 = 0.8A for 42 hours ... I do not know the parasitic current draw of my Yaris but a typical modern car is just under 0.1A so I don't think it is possible for normal parasitic current draw to have flattened my 12V battery when parked for a single day. However, something flattened my 12V battery in 42 hours ... so there may have been some sort of unusual parasitic current draw. My current theory is that Toyota tried to do an OTA update to fix a safety related issue with the e-Call system: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-XwY7m3xkybM.html I am talking to Toyota GB customer services about this theory. Toyota GB's current response is that the e-Call system was updated by Toyota Europe ... so Toyota GB have no information on the date when the e-Call OTA update was done and they are unable to investigate !?!??!?!?! I found this page on Toyota's website that recommends 60min per week in READY mode. You may also want to have a quick scan through some of the 27 pages of discussion of people with the 12V battery problem. mag.toyota.co.uk/coronavirus-toyota-hybrid-car-maintenance/ I combine my 60mins per week in READY mode with a weekly car wash ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Ch-L0JbbQUg.html I think this 92 page discussion on Toyota Owners club website shows just how widespread this problem is... www.toyotaownersclub.com/forums/topic/217673-12v-battery-maintenance-issues-etc/ My dealer has been very helpful and they have fitted the ODB cable free of charge so that I can easily plug a solar trickle charger in. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-o8MkFUPfdvQ.html I plug this in regularly ... not every day ... but most days especially if it is sunny. So I have got both "belt and braces" to try and avoid my 12V battery going flat again... - solar trickle charger plugged in regularly - weekly 60minute charge + car wash - NOCO GB20 jump starter stored in my car just in case !!!

I owned a 2018 Yaris Mark 3 Hybrid before I bought the 2022 Yaris Mark 4 in the video. The 2018 Yaris started reliably for 5 years even during COVID lockdown when it was only used once a week to go to the supermarket. I had a LandCruiser and it failed to start when the LandCruiser was 12 years old with the original factory fitted batteries. (The LandCruiser has two 12V batteries). The AA man told me he was amazed that the 12V batteries had lasted that long. He jump started me and told me that I MUST get new batteries immediately because the AA would not come out and jump start me again!!! From this discussion with the AA man I think you did well to get 6 years out of the 12V battery in your Yaris. I believe that an AGM battery is used in the Yaris because it is not safe to have a lead-acid battery inside the passenger compartment because of the fumes from a lead-acid battery are dangerous. So its good that you changed the 12V battery for an identical one. It's really interesting what you are saying about the car revving when stationary to charge the 12V battery. If I hear this in my car I will change the battery ... but hopefully my voltmeter will allow me to see the voltages dropping before I hear the engine revving. Since my 12V battery went flat I have discovered that a flat 12V battery is VERY common in the Yaris Mark 4. There is an 88 page (!!!) discussion on the Toyota Owners Club website www.toyotaownersclub.com/forums/topic/217673-12v-battery-maintenance-issues-etc/ and even a 27 page discussion on Toyota's website mag.toyota.co.uk/coronavirus-toyota-hybrid-car-maintenance/ Low mileage Yaris owners in particular are very likely to suffer from a flat 12V battery. I do UK average mileage but still my car failed to start after a single day without use. I have a theory that Toyota screwed up trying to update my car to fix a safety related problem with the e-Call system so I don't think my problem was caused by low mileage but by Toyota's poor systems for doing an OTA ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-XwY7m3xkybM.html There isn't a parasitic draw fault on my car ... Toyota have designed a flawed 12V system on the Yaris Mark 4. Unfortunately, Toyota just tell owners that it is their fault for not driving enough miles. Its corporate arrogance that will cost Toyota in the long term. Toyota HAD a reputation for building reliable cars .... they do not have that reputation any more. In order to ensure that my car does not fail to start again I ... (1) Charge the battery in READY mode for an hour each week while I wash the car ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Ch-L0JbbQUg.html (2) Use a solar trickle charger when the car is going to be parked on sunlight for more than 3 or 4 hours as recommended by my dealer ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-cSfik4yyXfo.html (3) Purchased a NOCO GB20 jump starter which I keep behind the passenger seat just in case the above do not work I think my Yaris Mark 4 is the best car I have ever owned ... but unfortunately it is also the worst car I have ever owned. And after owning Toyota's since 2005 ... it is my last Toyota. It's just a case of how long can I put up with wondering if the car will start each morning....

This is the link to the one that I bought on eBay ... but there are loads of similar ones from Amazon and other websites. www.ebay.co.uk/itm/266196406007 Cross fingers that you manage to avoid the 12V battery problem. The other things I am doing to hopefully avoid having another failure to start: - a weekly car wash + charge battery ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Ch-L0JbbQUg.html - solar trickle charger ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-o8MkFUPfdvQ.html - I have also bought a NOCO Jump Starter I live in the middle of the countryside and I am very dependant on my car which is why I am doing my best to avoid having another failure to start. The Yaris is both the best car I have ever owned ... but at the same time it is the worst !!!

@@Helpful-Stuff Thanks I also live in the sticks .I have brought a jump starter so will look up the meter :)

You way want to have a look at this video that I have made about a report on a Polish website that Toyota have accepted that there is a problem with the 12V battery in the Mark 4 Yaris. If your son in law's Yaris is still under warranty he may be able to get the battery changed under warranty. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-EHtg81kM-FU.html When my car failed to start the AA man measured the voltage at 9.45V. My car was only 10 months old and had not been used for one day. I drive around 7,000miles per year so my car is not a low mileage car. So in my view it should not have failed to start. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE--UkrUwpkePM.html

@@Helpful-Stuff Thanks the battery was not under warranty as over 5 years old. Anyway looked up a replacement and found just as cheap to buy one with same spec from local Toyota dealership. I got a 10 percent discount which made it comparable. Anyway new one came was same spec but physically slightly smaller. It still fitted in ok as height and depth were the same just slightly less wide. There was a plastic cover that is stuck in the car that fitted over the battery and a small hole in the cover and battery to fit the small tube for any gassing off from the battery. Anyway fitted and tried all working ok no resetting of anything and all seems to be back to normal. Ordered via the car registration and only one offered. Did find one same make but slightly bigger capacity and a touch wider so decided to go with the Toyota offered one just under £160 not cheap but well car would not work without one.

I think your son-in-laws car is a 2019 or earlier so it is a Yaris Mark 3. I owned a Mark 3 from 2018 to 2022 and it started reliably in the almost 5 years that I owned the car - even during COVID when I only used the car once per week to go to the supermarket. 12V batteries don't last forever so your new 12V battery should give you another 5 years of reliable starting 👍 All the videos I have been making about the 12V battery problems are for the Yaris Mark 4 ... my car failed to start after 1 day without use!!! In my experience your son-in-laws Mark 3 is a better car in terms of starting reliability than my Mark 4!!!

@@Helpful-Stuff Yep it is a mark three. I actually have had trouble with my Auris tourer during corvid. I left the rear open and the internal light drained the 12 volt battery. The battery was ok still and after a jump start when back at home I took it off and recharged it. Still ok now with the same battery. I think though especially newer cars with more electrical draw for things such as alarms when the car is off there is a vulnerability there. This can be a particular problem for low mileage users and something that should be addressed by Toyota. Perhaps someway of putting the low voltage battery on charge automatically when it gets low prior to it going completely flat. Or a solar panel to keep it charged up. Certainly when it happens for the first time it is perturbing as the display can do random things often showing up the engine warning light. It must be a known problem to Toyota and not beyond them to come up with a solution.

All Hybrids and EVs from all manufacturers have the 12V battery problem because they only need a small 12V battery because there is no starter motor ... but modern cars draw a lot of current when switched off and parked and this can drain the small 12V battery so that the car will not start after being parked for several days. And as you say this is more likely to happen to low mileage owners. After the AA had jump started my car my HUD wasn't working. It wasn't broken but an engineer had to stick a laptop into the OBD port and reset something to get it working again. From what people have said I think a failure to start affects the dashboard display and the electronics slightly differently in each car!!! Kia and Hyundai have developed the 12V Reset button. The 12V battery voltage is monitored when parked and if it drops below a certain voltage the 12V supply is turned completely off so that when you return to the car you press the 12V reset button and then the car will turn the 12V back on and the car will start because the 12V circuits were turned off and this stopped the battery from going flat. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3k7SSJecDUg.html I was watching a video about the MG app and this shows that the 12V voltage can be monitored in the app. Toyota are not really doing anything to help owners to monitor the 12V battery. There isn't even a 12V voltmeter on the dashboard. Toyota's response to the Yaris' 12V problem has been disappointing. Like you I can think of several possible solutions ... it would be nice if Toyota did something to help us manage the 12V battery with voltmeters on the dash and/or the app and maybe something like Kia/Hynudai's 12V reset button or a built in solar panel or maybe a free NOCO Jump starter with a new car!!!!

No .. I haven't noticed any change in my fuel consumption or the amount of fuel that I am buying. The petrol engine is only idling so the fuel consumption is very low. I do take precautions though by turning the heater off so that the petrol engine is only on for 158 seconds. I guess you have probably seen my video about combining a car wash and recharge ... but just in case this is the link: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Ch-L0JbbQUg.html I thought I would try and calculate how much fuel a typical car uses when idling ... so I Googled and I found out that the fuel consumption of an idling petrol engine is "0.6 litres / hr per litre of engine displacement" which if my calculations are correct means that 158 seconds for the 1.5 litre engine in my Yaris uses 0.04 litres = 0.009 gallons. So this does seem to confirm my guess that my combined car wash + recharge is using a very small amount of fuel.

I have asked the dealership where I bought my Yaris mark 4 about 5 months ago, what level would the voltmeter have to fall to for the car to fail to start. I can’t get a straight answer to the question. My wife and I do very few miles and since we’ve had the car have done only 230 miles. However, at least once a week I drive the car for 5 miles down the motorway and back again. In addition, I leave the car in ready mode for 1 hour 3-4 days after the motorway trip. I have to say I’m hugely disappointed having told the dealership that I do very few miles and given that an issue with the 12 volt battery has been known about for some time, I feel that transparency was not forthcoming at the time that the vendor was propounding the virtues of this car. Having bought 4 brand new Toyotas in the last 40 years I’m both surprised and disappointed with the company’s research and development, in allowing vehicles to come to the market with this deficiency.

I agree it can be very difficult to get detailed information about this problem. What I know from experience is: (1) My car failed to start at 9.45V (tested by AA man with a voltmeter connected direct to the battery) (2) The lowest voltage I have seen on my accessory socket voltmeter is 11.2V ... the car started OK So my best guess is that somewhere around 10V to 10.5V is the lowest voltage that will start the car. I think that where a customer, like yourself, made it absolutely clear that they drive very few miles per year then it is morally and possibly legally wrong to sell a Yaris Mark 4 hybrid. Have you considered contacting Trading Standards or Citizens Advice? I had a Yaris Mark 3 hybrid which started reliably for 5 years even during COVID lockdown when I was only using it once per week to go to the supermarket. So I know that Toyota can design a 12V system for a hybrid that copes with low mileage. The Yaris Mark 4's 12V system has a flawed design which means that it can fail to start after a single day without use (based on my own experience). Before my two Yariss I owned a LandCruiser for 13 years and almost 200K miles. So like you I used to be a big Toyota fan - they are not the worlds most exciting or flash cars but they were reliable ....

@@Helpful-Stuff Hi, from what I understand about battery depletion, the greater the number of depletions, the more the battery’s life is shortened. To date, the lowest I’ve seen on my voltmeter is 11.2v. And, of course, what exacerbates the issue problem, is the location of the battery. What I’m not sure of is whether the battery can be charged from the jump-start points under the bonnet. Might this seriously damage the car’s electrics? On the subject of consumer law and threatening some sort of litigation, I just want peace and tranquility in my few remaining years on this Earth.

How much a battery is degraded each time the car fails to start is another of those detailed questions I would love to know the answer to. - Do Toyota recommend that you get a new battery after the 3rd time a car has failed to start or the 13th time it has failed to start? - After a single failure to start is my battery OK? Its this sort of information that Toyota should be providing to customers instead of just saying "drive your car more". I am certainly not an expert but apparently you canNOT use the under bonnet 12V connections to charge the battery. There is some very useful discussion towards the bottom of page 1 of this 91 page discussion of the 12V battery issue on Toyota Owners Club website: www.toyotaownersclub.com/forums/topic/217673-12v-battery-maintenance-issues-etc/ Look for the comment by (1) DEVON AYGO on 2-Jan-22 and the next few comments which discuss the use of the under bonnet connections (2) CYKER on 3-Jan-22 about an access panel on the base of the rear passenger seat to the 12V battery but from the description it sounds very tight and fiddly and it may be easier to do (3) (3) DEVON AYGO on 3-Jan-22 describes how to unclip the rear seat to access the 12V battery. This is how my AA man accessed the 12V battery when my car would not start. You may want to have a look at a few random pages from this 91 page discussion to reassure yourself that you are not the only person with the 12V battery problem. Its a major issue. I totally understand about peace and tranquillity ... but I just thought I would mention that the legal route is an option for you. Good luck with your 12V battery 👍😀

Toyota are meant to be rolling out new test equipment & procedures for the 12V battery across Europe (which I assume includes the UK) and if a 12V battery fails then the 12V battery will be replaced under warranty. I have put more details in this video and there is a link to the original article in the video's description. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-EHtg81kM-FU.html It would be really interesting to know if UK Toyota Dealers have got new test equipment and using the new test procedures .... it would be great if you could ask your dealer and then leave a comment.

There must be something that you are doing right that the rest are doing wrong!!! I am doing a few more miles than you but my car failed to start after 1 day without use ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE--UkrUwpkePM.html ... I find it hard to believe that you were able to leave your car for 11 days without use!!!! I am currently making very slow progress with a complaint with Toyota GB Customers Services because I believe my problem may have been caused by a botched attempt by Toyota to do an OTA to fix a safety recall related to the e-Call system which drained my 12V battery. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-XwY7m3xkybM.html I had a Yaris Mark 3 which started reliably even during COVID lockdowns when it was only used once per week. My Yaris Mark 4 failed start when it was only 10 months old after 1 day without use. My view is that Toyota have botched the design of the 12V system in the Yaris Mark 4 which means that the it is very easy for the 12V battery to be drained. I have read that some people have changed the factory fit 35Ah battery for a 45Ah battery at Halfords. Maybe Toyota should change the battery in all Yaris Mark 4s to 45Ah. I don't think that Toyota will admit that there is a problem because they would then need to fix every single Yaris they have sold and that would costs a lot. If it was safety related then they would be forced to fix the problem but it isn't safety related so their strategy is to blame customers for not driving enough!!! Toyota need to wake up and realise that it is THEIR problem .... and that the strategy of blaming customers is causing a LOT of bad feeling that will result in Toyota losing their reputation for building reliable cars. I doubt I will buy another Toyota after owning Toyotas since 2005.

Thanks for the information that there is a 0.2V drop at the accessory socket voltmeter compared to the voltage measured at the 12V battery terminals. I knew there would be a drop but it is good to put an actual measured figure on it 👍 I think that in a Hybrid relatively little current is required to switch the computers on & switch the car on but the computers do need a good voltage from the battery. I think the most important feature for a Hybrid's 12V battery is the Ah. I believe that the Yaris Mark 4 has a factory fitted 35Ah 12V battery. A UK company (Halfords) will according to their website replace the 35Ah battery with a 45Ah battery. If I get more failures to start I will be replacing the 35Ah battery with a 45Ah battery. This should mean that it will take several more days for the battery to go flat if the car is not used.

@@Helpful-Stuff I just research yaris Hybrid battery and this come up S46B24RC Century ISS Active Stop-Start and Hybrid Auxiliary batteries are specially designed to satisfy the fuel saving and emission reducing benefits of vehicles fitted with Idle Stop-Start (ISS) or Hybrid systems. The range incorporates innovative design features and advanced raw materials to deliver superior cycling performance, high charge acceptance for rapid recharge in between engine off modes, and the extra power to run on-board electrics whilst the engine is switched off.

The description of the battery sounds good. I have just Googled and I believe it is a 45Ah battery which is better than the 35Ah battery factory fit battery. I would check the size ... there isn't much space under the rear seat for the battery. The first comment in this discussion on Toyota Owners Club says "Note battery tray will only accept a battery of L175xW175xH190" www.toyotaownersclub.com/forums/topic/212489-new-12-volt-high-power-battery-fitted/ The dimensions of the S46B24RC are Length: 238 Width: 128 Height: 202 Total Height: 227 ... so I don't think it will fit the battery tray in the Yaris. This video shows how to change the 12V battery ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-cdTEUrHs9Uc.html

A characteristic of all hybrids from all manufacturers is that they use a small 12V battery and if you leave it for 2 weeks in an airport car park while you are on holiday then the battery will probably be flat when you return from holiday. My Yaris Mark 3 Hybrid which I owned 2018 to 2022 started reliably for 5 years even during COVID when it was only used once per week. However, my Yaris Mark 4 failed to start when it was only 10 months old after ONE day without use. There is clearly a major problem with the Yaris Mark 4 which is a LOT worse than the normal characteristic of a Hybrid with a small 12V battery. I believe Toyota Europe have now finally recognised and will test and replace the 12V battery under warranty. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-EHtg81kM-FU.html I think your suggestion is a potential solution to the generic problem with Hybrids and the small 12V battery .... but in the case of the Yaris Mark 4 I think it would mask the root cause of the problem which is a bad choice of 12V battery fitted at the factory. Kia and Hybrid have come up with something called the "12V reset" button to avoid the 12V battery going flat in their Hybrids ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3k7SSJecDUg.html I think Toyota and all manufacturers need a solution to the 12V battery problem because a lot of people are saying they would prefer to go back to a petrol/diesel car which starts reliably.

Apparently Halfords will fit a 45Ah battery to replace the factory fitted 35Ah battery. When my Yaris failed to start and was taken to my dealer by the AA my dealer recharged the battery and recommended I buy a solar trickle charger ... so I bought one. I then Googled and started to read just how common this problem is with the Toyota Yaris Mark 4 .. there is an 88 !!! page discussion about this issue on the Toyota Owners Club. One common recommendation is to buy a NOCO jump starter ... so I bought one. Toyota recommend sitting in your car once a week for an hour with the car in READY mode to charge the 12V battery from the traction battery. Somebody on the owners club said he washed his car while it is charging to avoid sitting in his car and wasting an hour. I typically wash my car every week to 10 days so I started doing a weekly car wash + charge ... this is a "free" solution to me because I am going to wash my car anyway. I then read that some people are changing the 35Ah battery for a 45Ah battery at Halfords. I had already bought a NOCO jump starter and a solar trickle charger so I didn't really want to spend more money fixing Toyota's design problem. However, if the weekly wash + charge and the regular (but not daily) use of the solar trickle charge don't keep my 12V battery charged ... then I will be going to Halfords to get a 45Ah battery fitted. To be totally honest I feel very bitter about the way Toyota are handling this problem. It's a Toyota 12V design error that Toyota should fix but they won't because the cost of changing the 12V battery in all Yaris Mark 4 is too expensive. Toyota's reputation for reliable cars has trashed by the Yaris Mark 4. Incidentally I keep typing "Mark 4" because I had a Yaris Mark 3 for 5 years ... and the Mark3 started reliably for 5 years even during COVID lockdown when it was only used once a week. So Toyota can design a Hybrid that will start reliably ... but unfortunately the Yaris Mark 4 will not start reliably.

@@Helpful-Stuff wouldn't bother me to be fair I would go and buy the longest 12 volt amp hour battery I could fit in it

Voyez-vous une différence entre la tension mesurée à l’intérieur de la voiture et la tension au niveau de la boîte à fusibles ? (Google Traduction)

You are quoting voltages measured at the battery terminals when there is no current being drawn from the battery. That is not what I am measuring with a voltmeter plugged into the accessory socket. There is a lot of wire between the battery under the rear seat and the accessory socket so the voltage will not be the same at the battery and at the accessory socket. The voltage measured at the accessory socket will always be lower than the voltage measured at the battery. The car is in accessory mode so some of the car's 12V systems & computers are switched on ... the most obvious being the screen and multimedia system. These draw current from the 12V battery and will reduce the voltage. Toyota changed my 12V battery a couple of months ago so I now have a brand new 12V battery. I have obviously kept my voltmeter plugged into the accessory socket and I am seeing voltages about 0.5V higher than shown in this video. Most of the time I am seeing 12.3V in accessory mode ... occasionally it is as high as 12.5V and occasionally as low as 12.1V and this has been consistent over the last 2 months since the battery was new. The fact that a brand new 12V battery has never shown a voltage higher than 12.5V when measured at the accessory socket confirms that voltages measured at the accessory will always be lower than the voltage measured at the battery terminals with nothing connected to the battery.