Mooly

Well up to a point but the ECU, the immobiliser, the receiver for the locking and unlocking from the key and so on are all powered on a car like the old Corolla. The secret is in micro power design and I think this is where the failings are. Manufacturers have just totally underestimated how lead acid battery technology is unsuitable for this kind of application.

That is a logical assumption but speaking from real experience it is not always so. My fathers old Corolla did as few as 500 miles a year for a couple of years and only a 1000 or so in other years from around 2014 to 2019. It stood outside on the drive and never suffered any battery issues and in fact last had a battery in 2012 due to suspicion of leakage. The car is 21 yr old next year. I think you could be right on that and this is something that again would be easy for a proper investigative test. Again we need to see current into the battery when beginning charging from a known partially discharged battery state into an otherwise healthy (new) battery. An ICE with alternator can deliver upwards of 70 amps and more at little over idle speed and not much lower than that at idle. Remember it can cope with lights, heated window, wipers, blower etc at idle without the battery entering a discharge condition. I remember reading decades ago that an alternator can never fully charge a battery and at the time I couldn't understand why. Surely it can. Only in later years have I come to realise what was probably meant by that blanket statement and it is that the alternator with its fixed 14 or 14.4v output will quickly bring a battery to a high state of charge but would then need to run for a very long time (perhaps 30 hours or more) to fully charge the battery and of course that never ever happens. Does anyone know the current output capability of the DC/DC convertor used in the hybrids for charging the 12v battery and powering all the 12 volt equipment? That is another missing piece of information to me.

I can't recall seeing one. Current draw logged over a decent time period that the car is inactive is what is needed rather than just battery voltage.

Exactly, at the end of the day you want (and should expect) something that just works. The myriad threads and posts on these issues show that goal hasn't been met and yet there is no definitive reason as to what is going wrong. It would be so easy to rig a test vehicle up with a current monitor (measuring voltage just doesn't really cut it here) and log the discharge rate over say 7 days. I've never seen anything like that published. Its pretty obvious that this battery issue is widespread across not just Toyota but other makes and models as well. There is nothing to beat 'customer usage' to find out design defects that just don't show in design and development despite months of testing and millions of miles covered in development. I don't believe there is a easy fix for this although I would bet next generation vehicles will be much improved. Low power (micro power) design of the background electronics is what is needed possibly along with a more aggressive charge regime when it is in use. That is what needs to happen.

I suspect the cause is a lowish constant current draw that causes battery deterioration. New battery, 100% capacity and you take 10% out of it by leaving it for a couple of days. You drive for an hour and it is back to 99%. You leave it a day and its down to 97%. A short run and its back at 98% and so on. Its a slow but constant decline day after day. This type of battery would need a prolonged float charge to bring it back to 100% but that would only work provided the battery was never allowed to reach a low state of charge. Once the charge is down to the 70% or less region (and has been left like this for a long time) you are into permanent damage and a loss of capacity that can never be recovered. This has long been suspected and I would go as far as to say it would be worthwhile for any new owner (new car just delivered) to do a real world discharge test on the battery to make sure it appears to have its rated capacity. I appreciate that is not easy for most owners as it would require a known load (an electrical consumer) being run and monitoring the battery voltage. For example an old single conventional headlight bulb of 55 watt rating would draw just over 4.5 amps and run for around 7 hours before a 35Ah battery was fully discharged. You shouldn't go that far in a test but leaving something like that for 3 or 4 hours should not see the loaded battery voltage fall below around 12.1 volts. If the battery on a new car can not do this then its duff from day #1 Having done a test like this the battery should then be fully charged back to 100%

So we assume it was fully charged although we have no idea what the actual capacity vs the rated capacity is. So now totally discharged over say 18 hours. What is the rated capacity of these 'smaller' batteries? I recall around 36Ah give or take. If your battery were at that capacity then you would have to be pulling a couple of amps for those 18 hours and that is not insubstantial. It would generate a lot of heat if something were drawing current. I think think the most likely scenario is just that the normal lowish (but still excessive in the scheme of things) background current draw has caused the battery to deteriorate over time. Something like your dashcam might be contributing to this because even when 'off' it may still have a quiescent current draw. Only way to know is to measure it. It doesn't need much on a 24/7 basis to kill a battery. The battery technology used (lead acid type that is a couple of century's old) is not suitable for this type of use.

A 2010 model isn't really that ancient technology wise and it is such things as the idle speed setting would be lost. An empty battery in the majority of cases simply sees a low resting voltage of say 10 or 11 volts sag dramatically as the starter is operated but even a very low voltage is enough to keep the ECU powered and prevent it doing a global reset of everything.

The problem with 'modern' cars is that the ECU will loose the long term learned values for optimum running of the engine if you disconnect the 12 volt battery. The result is it can start and run badly for several miles following a disconnect until the ECU relearns the optimum settings. It carries on 'learning' and optimising all the time from then on.

Thanks for the update, and pleased to hear you finally found the cause. Well done.

If this was working correctly up to the point you installed a new amp and speakers... well I think you have to go back over that work and if necessary revert the changes and see where that gets you. I have no idea (never having seen one) how the amp interacts with the existing wiring and vehicle electronics but given that you say it was 'plug and play' and knowing how interconnected all the systems are in a modern car I would be wondering if some data or clock line was being corrupted somehow and that that was inhibiting the immobiliser.

Well they look the similar as far as I can tell (and its not always easy working off pictures) but the top left of each seems to have a different profile. Is that an artefact of the image though. Does the key turn the door lock? although its possible for it to turn in one and not another.

As far as I know the key should just be a mechanical fit and that alone 'unlocks' the barrel. The transponder simply enables/disables the ignition. So a mechanically correct key should do everything apart from actually allowing everything to fire up. Are you 100% sure the key is the correct one? Has it worked in the past? Do they look identical?

Certainly on the older Auris and the charging is under constant control with the alternator changing from a nominal 14.4v down to around 12.5 volts. https://www.toyotaownersclub.com/forums/topic/186724-stop-start/?do=findComment&comment=1492865 Whichever way you look at it, the 12 volt battery in any car has to fall under the 'cyclic' use tag. The one thing the Auris has is a sensor (a very very low value resistor) in series with the battery feed and this resistor develops a volt drop as current is drawn. This is the little 'box' on the battery terminal clamp. The resistor value is so low that I think the drop is just 0.1 volt per 100A but that is enough for suitable electronics to calculate the energy removed from the battery (not so much in amp hours but by looking at Coulombs as a unit of charge) and it can therefore calculate how much energy to put back in. It is very accurate and works well. If you have a partly discharged 12 volt battery and you find the voltage immediately rises to around 14.4 or higher when put on charge then that implies that either you have a very very high capacity charger (cable of delivering many 10's of amps) or the battery has significant internal resistance (deteriorated). Again on the Auris, a discharge test of say headlights, heated window, fog lights etc all being left on without the engine running pulls a very high current from the battery. Fwiw a fully charged and healthy battery will support that level of loading for a considerable time. Where is gets interesting is when you start the car after doing that. The loading is so high on the alternator (so it becomes very hard to spin round) that the engine immediately stalls. This is because the battery is taking all the current the alternator can deliver which could be as high as 50A or more and the learned idle position of the engine can not support that extra unexpected mechanical loading. That high current soon tails off and the more deteriorated the battery and the quicker it does so.

Nice little vid on the Castrol Ultra Clean: https://youtu.be/KUIPCOAE7DI

Its Castrol 'Ultra Clean' 10/40 grade. At least it is holding any contamination in suspension. Shining a torch in the filler hole and having a good look and it is all super shiny clean everywhere, it really does look like brand new with no deposits of anything visible anywhere. I've started giving it a little squirt of acceleration as soon as possible from cold now. I don't like doing that but it seems to help I suspect. Nothing outrageous, say up to 4k in 1st and 2nd and then drive more normally after that initial burst. And some days it just seems to run so well, and today was one of those days. You'll get there with it Tony 😉just leave it a bit longer.