12 volt battery mysteriously losing charge & car won't start

For the second time. our Corolla wouldn't start today (Thursday). Fortunately the car was at a garage with a booster pack, so we were able to start the car and drive it for a while to charge the Battery. Last Saturday we did about 60 miles, then on Monday we did 4 miles and Tuesday we did 18 miles. The car  stood for three days and then would not start.  This is worrying: for example if we go on holiday and leave the car at the airport car park for a period of time, it's highly likely that the car won't start on our return. The car is awaiting a call from the dealer to do some overnight testing of the Battery, but does anyone know of a fix? If not, I am considering rejecting the car because it is not acceptable that this problem occurs and could be serious if we are on the Moors with our dog in the boot and no 'phone signal to call for help.

The dealership can run it though a Battery tester to check the health as well as the overnight test. 
 

depending on the Battery type, they can be damaged if they have gone flat and never recover fully so have to be replaced. 
 

a normal healthy Battery that’s been driven as yours should last at least 2-3 weeks when the car is locked and not used. 

16 hours ago, Pannett said:

For the second time. our Corolla wouldn't start today (Thursday). Fortunately the car was at a garage with a booster pack, so we were able to start the car and drive it for a while to charge the battery. Last Saturday we did about 60 miles, then on Monday we did 4 miles and Tuesday we did 18 miles. The car  stood for three days and then would not start.  This is worrying: for example if we go on holiday and leave the car at the airport car park for a period of time, it's highly likely that the car won't start on our return. The car is awaiting a call from the dealer to do some overnight testing of the battery, but does anyone know of a fix? If not, I am considering rejecting the car because it is not acceptable that this problem occurs and could be serious if we are on the Moors with our dog in the boot and no 'phone signal to call for help.

This seems to be a running theme, to a certain extent on Corollas, and perhaps more so on the Yaris.   Out of interest, is yours a 1.8 or 2.0?

I think that I have just kind of accepted that this is an unwelcome characteristic of the car.   I already had an Optimate smart charger, from biking days, so I've wired the lead to the Battery.   I give it a top-up charge if I'm not using the car for a few days.   My Optimate is really intended for bike batteries - charges at 0.8A max - but the Corolla Battery is only 45Ah and it works fine.

I also carry a Li-ion jump starter in the car.   They are small and light.   It doesn't need to be very powerful because the 12v Battery doesn't actually start the car (as in turn over the engine), it just initialises the systems.

12v Battery issues are relatively commonplace on hybrids, and affect other makes as well. 

15 minutes ago, FROSTYBALLS said:

12v battery issues are relatively commonplace on hybrids, and affect other makes as well. 

That may be so although, as a by-the-by, my brother has a Mitsubishi Outlander PHEV (2015) that has never had 12v Battery issues. 

I believe that some Hyundai/Kia hybrids have a button on the dash that gives the 12v Battery a boost from the traction Battery in case the 12v battery is too low to start the car?   I'm sure that I have seen same, probably in a Hyundai, although I don't remember the details.    That does seem like an acknowledgement of a problem but at least with a solution. 

All I would say, as a (long time) former electrical/electronic engineer, is that if this is a common problem then it is a symptom of poor design. 

I am not suggesting that other car manufacturers are any better, mind!

1 hour ago, SDR said:

 

I believe that some Hyundai/Kia hybrids have a button on the dash that gives the 12v battery a boost from the traction battery in case the 12v battery is too low to start the car?   I'm sure that I have seen same, probably in a Hyundai, although I don't remember the details.   

Yes, I was looking at Hyundai's a while ago - it seemed to be a virtual Battery without an actual real 12V one fitted.

The computer sets aside a portion of the main big Battery to use as a 12V one.

If it goes flat, you push the button and the computer just allocates a different part of the big Battery to use as a 12V one and the car starts up. Provided you have power in the big battery.

2 hours ago, FROSTYBALLS said:

12v battery issues are relatively commonplace on hybrids, and affect other makes as well. 

My Yaris had a tiny little Battery under the back seat, so hardly any power in it.

The newer models do seem to be better, my Corolla has a decent size Battery that you would be likely to find in a normal petrol car.

Maybe Toyota has learned from all the issues from having small batteries.

That’s not the case in Hyundai kia cars, they do have physical small 12v batteries similar to Toyota hybrids and they do suffer similar faith in some models. The option to recharge from the traction Battery does work on evs as I tested it and no need to press a button, the car does it automatically when it’s necessary, however on Toyota hybrids the traction batteries are so small that this is not an option.  
The op has its Battery dead and even if it’s showing ok on the dealer tests he should request a new Battery replacement. It seems this Corolla doesn’t get enormously drive time to maintain good battery charge. If we do short trips and each time the car is on for less than a 30 mim this will kill the battery, plus the latest models has added connected services, all that equals premature battery failure 🪫

29 minutes ago, sportse said:

Yes, I was looking at Hyundai's a while ago - it seemed to be a virtual battery without an actual real 12V one fitted.

The computer sets aside a portion of the main big battery to use as a 12V one.

If it goes flat, you push the button and the computer just allocates a different part of the big battery to use as a 12V one and the car starts up. Provided you have power in the big battery.

So that's how it works!   At least I remembered the button!    Better than having to use a jump pack or call recovery, for sure. 

Hopefully, the traction Battery shouldn't go flat for a long time as there isn't any drain on it when the car is switched off (or, at least, there shouldn't be as far as I can see) and Li-ion batteries have a low self-discharge rate.

This week, I bought a little Battery tester to keep an eye on my wife's Fiat 500. The car is 9 years old now and used exclusively for town driving, so I know the Battery has to be approaching the limit of a reasonable life expectancy.

According to the tester, the OE Battery in the Fiat is still in good health! I then tried the same tester on my Corolla, which is under 3 years of age. Couldn't do the test - not enough charge to begin.

Before getting the tester, I've checked my Corolla battery with a DVM a few times and it was alway low, regardless of whether it had been stood or not. I believe there's a fundamental issue with the charging system on these cars; it's simply not as effective as an alternator at keeping the battery topped up. Combining this with the fact that the batteries fitted in these hybrids are low capacity (because they don't have much to do) and the parasitic draw while standing seems relatively high (from the tests I did a couple of years ago), it's not difficult to understand why there are issues. What IS difficult to understand is why on earth Toyota, with all of their hybrid vehicle experience, and their hard-earned reputation to protect, have a) allowed this to happen on a recent model and b) have seemingly no interest in rectifying at least one of the causes through design improvements. I feel sure that addressing just one of the things I've mentioned above would yield a massive improvement.

I could do with some advice.

I took delivery on a few 1.8 Touring Corolla. First day of ownership, I parked in a car park for a few minutes and was listening to the radio, you guessed 12v warning message. A whole weekend of 12v warnings, The car had to go back to the garage with multiple other issues, they acknowledge Battery was discharged, and they put it on a trickle charger. They pledged it would be fine. Car is back with me, I do lots of short journeys (why I bought a hybrid rather than a diesel). Park in a car park for a few minutes, and listen to the radio, you guessed it 12v warnings.

Am I supposed to trickle charge the car every week, so the Battery doesn't go flat? Do Toyota genuinely think these cars are fit for purpose?

What with the 12v and all the other issues I've had, I don't see any other resolution, but to reject the car within 30 days and get a full refund. It's a shame as I like the car but have lost confidence. 

If you are parked up listening to the radio, leave the car in park and 'ready' mode i.e. with the ignition on. In 'accessories' mode you will get a five minute voltage warning and then it will shut down to protect the 12v Battery. In 'ready', if you turn off the ventilation, the engine will probably only run once every 20 mins.

4 minutes ago, RabButler said:

If you are parked up listening to the radio, leave the car in park and 'ready' mode i.e. with the ignition on. In 'accessories' mode you will get a five minute voltage warning and then it will shut down to protect the 12v battery. In 'ready', if you turn off the ventilation, the engine will probably only run once every 20 mins.

Thanks for the suggestion but, I don't even get 5 mins, and what's the point of accessory mode. How can this can be fit for purpose?

It is fit for purpose. It's a hybrid. That's how they work. Read the manual.

2 hours ago, Red_Corolla said:

I then tried the same tester on my Corolla, which is under 3 years of age. Couldn't do the test - not enough charge to begin.

Before getting the tester, I've checked my Corolla battery with a DVM a few times and it was alway low, regardless of whether it had been stood or not. I believe there's a fundamental issue with the charging system on these cars; it's simply not as effective as an alternator at keeping the battery topped up. Combining this with the fact that the batteries fitted in these hybrids are low capacity (because they don't have much to do) and the parasitic draw while standing seems relatively high (from the tests I did a couple of years ago), it's not difficult to understand why there are issues. What IS difficult to understand is why on earth Toyota, with all of their hybrid vehicle experience, and their hard-earned reputation to protect, have a) allowed this to happen on a recent model and b) have seemingly no interest in rectifying at least one of the causes through design improvements. I feel sure that addressing just one of the things I've mentioned above would yield a massive improvement.

 This is, I think, a very good summary of the situation.    It is also why, as a new owner, I have already started using a smart charger and have a jump pack in the car.

Being new on the forum, I don’t want to get a reputation for Toyota-bashing.   Especially as I think that some aspects of the design, e.g. the HSD, are very good indeed.   BUT, with an electrical/electronic engineering background - albeit a long time ago now - I also find it difficult to understand how this has been allowed to happen.

Look at the systems that are live when the car is switched off.   Calculate the current draw for each.   Add up 🤔....   Fit a Battery that should be good for at least a month without the car being used, preferably longer, with a charging system to match.   If the current draw is too high to make the latter practicable, do something about it.   Restrict certain systems.   Really, rocket science it ain't.    It's just lazy engineering. 

Probably not entirely fair to say that Toyota aren't doing anything about it though.    After all, I’m sure that I have read somewhere that dealers are selling solar chargers that plug into the OBD port?   Yep, we've sold you a car with an inadequate electrical system but for £50 we have a solution 😁

10 hours ago, W1P30UT said:

Thanks for the suggestion but, I don't even get 5 mins, and what's the point of accessory mode. How can this can be fit for purpose?

 

It's not meant for more than very brief, occasional use (because it would cause the problems you're having if used too often I guess).

It can be deactivated in the vehicle settings on the multimedia screen if you're having trouble with it.

10 hours ago, W1P30UT said:

they put it on a trickle charger. They pledged it would be fine. Car is back with me, I do lots of short journeys

My Mercedes diesel had a massive stop/start Battery.  After a few minutes in accessory mode it would switch off.

Yaris Cross admittedly but same size Battery.  Regarding lots of short journeys.  Over a week you may accumulate the 'magic' 60 minutes in Ready mode.  Unfortunately,  in my experience,  that is not sufficient. 

I have found that a series of short journeys over a week results in a linear drop in voltage with short charging spikes insufficient to maintain the voltage.  Two or 3 journeys for 60 minutes total is fine. 

PS, my car will be at the 20 000 mile point next month, I will do a 75 mile journey and then park up for 2 weeks; that will be the acid test.  I have had 3 previous 2 week breaks without issue. 

41 minutes ago, Don Mac said:

It's not meant for more than very brief, occasional use (because it would cause the problems you're having if used too often I guess).

It can be deactivated in the vehicle settings on the multimedia screen if you're having trouble with it.

Yes, I never use accessory mode as the batteries are too small and not designed to run things.

I've owned 3 Toyota hybrids now - Yaris, Auris & Corolla and always just put the car into EV mode and turn off the climate control. You have 5 seconds or so to do this after pressing the start button before the petrol engine starts.

Once in EV mode with climate switched off, the car will run for ages without the engine turning on. When the charge level in the hybrid Battery drops the car will start up the petrol engine and recharge it a bit before switching off again. (The cycle will repeat for weeks if you have enough petrol.)

When we weren't able to drive far a few years ago, I would do this and read the paper for 30-60 minutes. That's all that's needed to keep the 12V Battery topped up if you've only driven 5 miles in a week.

All the time the car is in ready mode the 12V Battery is being recharged. You don't have to take the car for a drive to recharge it like other normal cars.

12 hours ago, W1P30UT said:

Thanks for the suggestion but, I don't even get 5 mins, and what's the point of accessory mode. How can this can be fit for purpose?

 

I think the Battery isn't good, I once had a MK3 Yaris with 35ah and it could do 2-3 times ACC mode listening to music. Measure the Battery voltage, if not holding charge, change it to a bigger capacity if possible. 

ACC mode or ON mode even on diesels or petrols never been the right way to use 12v power in any vehicle but just for short time, seconds not minutes. Even adding air to your tyres using compressor or charging your phone you should start the engine on ice cars or start the hybrid system in ready mode on hybrids and evs. 
It seems to me people who has Battery problems simply doesn’t use correctly the cars or often enough.
There is nothings wrong with the design or functionality on charging system of these cars, it’s just the Battery capacity, the connected services and lack of use. The only true thing here is that any car no matter ice, hybrid or ev should be able to start after 3-4 weeks of inactivity with healthy Battery. 
The problem is that the batteries quickly became unhealthy as per the reasons above. 

The 12v battery in any Toyota hybrid is responsible for all electronics and accessories except AC and e motors., even when the car is in ready mode.  
12v battery always supply power to everything and get charged by the inverter which work’s exactly the same way as alternator in standard ice cars. 
Low or dead 12v battery will keep draining your traction battery, keep engine running unnecessary for longer time and reduce your efficiency plus even after 1 hr in ready mode or long drives when you stop and turn off your car , shortly after you won’t be able to start. 
Just push dealers for brand new battery under warranty and take extra care afterwards. Toyota hybrids are the best cars currently, no diesel, no evs. 👍

 

Yeah there's almost no reason to use anything other than Ready mode when the car is in use, even when sitting in it waiting or listening to music.

The Accessory mode is a vestigial throwback like the simulated idle creep and I can't think of any reason or purpose it serves on the hybrids; Probably still included because all cars that came before had it and no other reason.

When you park up, just put it in park and don't turn the car off. Or if you want to park without your DRLs on, turn the car off, wait a second, then hold the brake pedal and turn it on again and don't shift it out of P.

16 minutes ago, Cyker said:

Yeah there's almost no reason to use anything other than Ready mode when the car is in use, even when sitting in it waiting or listening to music.

The Accessory mode is a vestigial throwback like the simulated idle creep and I can't think of any reason or purpose it serves on the hybrids; Probably still included because all cars that came before had it and no other reason.

When you park up, just put it in park and don't turn the car off. Or if you want to park without your DRLs on, turn the car off, wait a second, then hold the brake pedal and turn it on again and don't shift it out of P.

Each to their own, but the idle creep is very important to me, it's what sold me on a Corolla as a car that drives like a proper slushbox without the price premium. 😇I don't want to have to dance between pedals every time I want to nudge forward a bit. For the same reason, I'm awfully glad that brake hold stays off after I've turned it off - it's not what I want as a default behaviour.

I’ve mentioned this before, my 2019 Corolla has never suffered from these issues; it’s now at 25k at 4.5 years old. On a number an occasions the car has stood for two to three weeks and still started instantly. I’ve noticed on the forum that most issues appear to be on 2021 car onwards.

I don’t know what has changed other than more tech, including more connectivity.

On 5/24/2024 at 10:44 PM, SDR said:

Look at the systems that are live when the car is switched off.   Calculate the current draw for each.   Add up 🤔....   Fit a battery that should be good for at least a month without the car being used, preferably longer, with a charging system to match.   If the current draw is too high to make the latter practicable, do something about it.   Restrict certain systems.   Really, rocket science it ain't.    It's just lazy engineering. 

Absolutely 100% agree and would also add that lead acid Battery technology is not suited to this kind of use of constant current draw discharge and short (and what amounts to 'cyclic') recharge regimes. 

The way forward is micropower circuit design. My 13 yr old 'Dumb Phone' runs for between two and three weeks between recharging and all with a 3.7 volt Battery of less than half the volume of a small matchbox.

I can go out to my (non Hybrid) Auris and turn the ignition on and turn on headlights, fog lights both front and rear and also heated rear window and then walk away for 15 minutes and come back and know the car will start as normal. The Hybrid owners say the Battery 'goes flat' if you listen to the radio for a few minutes... which really is only proving the battery is down to a few % capacity.

On 5/24/2024 at 10:44 PM, SDR said:

Really, rocket science it ain't.    It's just lazy engineering. 

100% yes to that.

Accessory mode and On drain a LOT of power on new cars as there are so many more computers, and a lot of the tech is old and more power-hungry than more modern stuff as it has to go through road-worthiness certification which takes ages; Another thing is the radio transmitters for things like the keyless system, which burn a surprising amount of power.

This is why e.g. the Battery in cars with powerful infotainment systems are twice the size of normal car batteries and weigh the same as a small elephant, and I've even seen some cars which have two 12v bateries - One normal starter-type 12v for... the starter, and a gigantic  12v 'leisure' Battery - of the sort that normally power caravans! - to power all the infotainment stuff!

I think it was a miscalculation on Toyota's part - I can see why they thought it was a clever idea, as the smaller Battery saves weight and it otherwise plays no part in running the car as the traction battery handles everything once it's on, but this is a not a new problem for them and they really should have come up with better mitigation strategies by now.

But there is just no reason to use the Accessory and On modes with the hybrids - Unlike a normal car the engine won't be running all the time, which was the only reason to use the accessory mode when waiting in older cars, to avoid slowly gassing yourself and anyone nearby and wasting loads of fuel, neither of which apply with the hybrids!

Some stuff is a genuine problem, but rejecting the car because the 12v battery died because you were using it on Accessory mode repeatedly is like an auto driver rejecting a manual car because it makes a horrible noise when they try to put it in gear because they aren't pressing the clutch.

The OP's car will need a new battery now as it's probably shagged from being abused so much, but you'll probably be able to trick them into doing it under warranty as so many Yaris owners had this problem; Once you do, give it a run or park up somewhere for a while to give it a good headstart charge, and don't use Accessory mode in it ever again!

1 hour ago, Red_Corolla said:

Each to their own, but the idle creep is very important to me, it's what sold me on a Corolla as a car that drives like a proper slushbox without the price premium. 😇I don't want to have to dance between pedals every time I want to nudge forward a bit. For the same reason, I'm awfully glad that brake hold stays off after I've turned it off - it's not what I want as a default behaviour.

Yeah I do wish they'd put in more customizability for things like this - Everyone has different preferences and none of these are right or wrong, and with everything being computer controlled now there's no physical reason why they couldn't let you change how all these default behaviours work and save it to a quick-selectable profile or something.

A lot of the new stuff in my Mk4 I've embraced, but my colleague would absolutely hate them and having to go through a 10minute checklist routine like a pilot to turn everything he wants off or on every time he wants to use the car would be an absolute deal breaker.