12v battery maintenance, issues, etc.

[nlee]

18 hours ago, robo1 said:

The 12v battery is charged from the traction battery so it gets charged whenever the car is in ready mode irrespective of if the engine is running. No one seems to know at what rate the traction battery charges the 12v battery but I suspect it’s a lot less than an alternator hence the flat batteries. 

During driving, the voltage modulates between around 14.5v when charging, and around 12.7v when maintaining, depending on what the car's brain thinks it needs.

The graph below shows the voltage increase in the early hours when the traction Battery scheduled charge starts (only a top-up, so only about 30 mins), then a journey in the morning where the full journey is around 14.6v, then one in the afternoon where it starts at 14.6v but quickly drops to maintenance around 12.7v.

I never been able to fathom why it always jumps up to 14.7v after I pull up outside the house just before I reverse onto the drive.

[Rigsby]

Just a reminder for those who are having these issues, make sure your DCM has had its software update.

This was a TSB last year that was done to resolve a number of issues, including the 12v Battery becoming flat when left for an extended period of time.

It may or may not be the cause of the Battery draining, but it’s certainly a good starting point, ask your  dealer to check if your car has had the update, at least you can rule something out.

[TonyHSD]

3 hours ago, nlee said:

During driving, the voltage modulates between around 14.5v when charging, and around 12.7v when maintaining, depending on what the car's brain thinks it needs.

The graph below shows the voltage increase in the early hours when the traction battery scheduled charge starts (only a top-up, so only about 30 mins), then a journey in the morning where the full journey is around 14.6v, then one in the afternoon where it starts at 14.6v but quickly drops to maintenance around 12.7v.

I never been able to fathom why it always jumps up to 14.7v after I pull up outside the house just before I reverse onto the drive.

Probably because when starting the car the 12v Battery gets loaded and voltage drops and therefore it will receive full power charging. 

[Terry10]

8 hours ago, Rigsby said:

Just a reminder for those who are having these issues, make sure your DCM has had its software update.

This was a TSB last year that was done to resolve a number of issues, including the 12v battery becoming flat when left for an extended period of time.

It may or may not be the cause of the battery draining, but it’s certainly a good starting point, ask your  dealer to check if your car has had the update, at least you can rule something out.

Hi, Does this apply to H E V as well as plug in???????

Also, can you tell me what the T S B number is?
Thanks Terry
 

[Rigsby]

4 minutes ago, Terry10 said:

Hi, Does this apply to H E V as well as plug in???????

Also, can you tell me what the T S B number is?
Thanks Terry
 

Yes, I have a HEV and I got a letter to tell me about it.

Dont recall the TSB number, sorry.

[Terry10]

Thanks, I shall email my dealer.

regards Terry

[Rigsby]

1 hour ago, Terry10 said:

Thanks, I shall email my dealer.

regards Terry

There is a thread on this forum under the heading of 

Recall for DCM 2022 Rav4 Hybrid

 

Item 3 sates Auxiliary Battery may become discharged

[ernieb]

On 5/3/2024 at 10:31 PM, Rigsby said:

There is a thread on this forum under the heading of 

Recall for DCM 2022 Rav4 Hybrid

Item 3 sates Auxiliary battery may become discharged

Affected cars should have had the letter and additionally it should have been picked up during the booking for a service.

[Rigsby]

2 hours ago, ernieb said:

Affected cars should have had the letter and additionally it should have been picked up during the booking for a service.

Agreed, they should had been contacted, but worth asking the question.

[ToyotaFanDriver]

Thanks Nigel, I appreciate the information! 👍

[MrBee]

I have a quick question on this, sorry if it's been covered before. 

I have a 2020 HEV that has suffered with flat batteries Dec/Jan after 2/3 weeks of no use. I'm thinking of changing to the PHEV. Does this model have the same issue? 

Thanks. 

[philip42h]

53 minutes ago, MrBee said:

I have a quick question on this, sorry if it's been covered before. 

I have a 2020 HEV that has suffered with flat batteries Dec/Jan after 2/3 weeks of no use. I'm thinking of changing to the PHEV. Does this model have the same issue? 

Thanks. 

Yes, exactly the same 'feature' - it's common to all Toyota hybrids (and probably most EVs).

It occurs through lack of use / too much standing time but is exacerbated by other issues which vary by model / production date - these need to be addressed with the dealer as appropriate.

The PHEV has a slightly larger auxiliary Battery so will potentially 'stand' a little longer. Using remote access functionality will place a greater draw on the auxiliary Battery. It is possible to use the remote preconditioning feature to effectively put the car into 'Ready' and top-up the auxiliary Battery so with care and planning the driver may be able ameliorate the problem of a long stand.

[MrBee]

3 minutes ago, philip42h said:

Yes, exactly the same 'feature' - it's common to all Toyota hybrids (and probably most EVs).

It occurs through lack of use / too much standing time but is exacerbated by other issues which varying by model / production date - these need to be addressed with the dealer as appropriate.

The PHEV has a slightly larger auxiliary battery so will potentially 'stand' a little longer. Using remote access functionality will place a greater draw on the auxiliary battery. It is possible to use the remote preconditioning feature to effectively put the car into 'Ready' and top-up the auxiliary battery so with care and planning the driver may be able ameliorate the problem of a long stand.

Many thanks for the quick response. It is annoying. This December we were away for a bit and did not use the car for 3 weeks. The 12v was so flat that the jump start booster did not work. Had to put it on a Battery charge overnight. 

That could be a real pain if you left the car in a long term car park for a winter holiday. 

[Roy124]

37 minutes ago, MrBee said:

The 12v was so flat that the jump start booster did not work. Had to put it on a battery charge overnight. 

As a matter of interest,  how long did you have the booster connected before you tried to start the car?

[MrBee]

11 minutes ago, Roy124 said:

As a matter of interest,  how long did you have the booster connected before you tried to start the car?

I tried it a couple of times with the booster fully changed to empty 

[Roy124]

25 minutes ago, MrBee said:

I tried it a couple of times with the booster fully changed to empty 

Thank you.  I hafmd heard that leaving the booster connected for a few minutes before trying to get Ready mode made a difference.   Not sure if that is true.

[philip42h]

2 hours ago, Roy124 said:

Thank you.  I hafmd heard that leaving the booster connected for a few minutes before trying to get Ready mode made a difference.   Not sure if that is true.

Logic suggests to me that the converse would be the case - connect the jump start pack and immediately press the brake pedal and Start button to get into Ready mode.

You'd want to get into Ready mode and not attempt to charge the 12V auxiliary Battery. Once you are in Ready mode the 12V auxiliary Battery will be charged from the traction Battery. 👍

The jump start pack will have a relatively small capacity so if you leave it connected to a relatively discharged 12V auxiliary battery for any significant length of time it will dump all its available charge into the battery leaving neither with sufficient voltage to get into Ready mode.  👎

Or, at least, that's how it would appear to me ... 😉

[ernieb]

Agree with @philip42h, connect and go into READY mode immediately.

[Cyker]

This is one of those "It depends" things - If the 12v Battery is just discharged but not actually dead, charging it up for a bit can help, esp. in normal cars where having the current capacity of the 12v and the jump pack can help crank the started easier; This was advice more common for us DERV people, where the diesel starter usually needs a LOT more current than most petrols to get it going.

If the 12v is super dead though, it will suck so much power out of the booster there might not be enough to actually start the car - It's one thing that makes me have 2nd thoughts about getting the weakest Noco booster pack, as I'm wondering if it has enough current capacity to stave off Battery sag and still power up the ECU long enough for the contactors to engage!

I reckon with the Toyota hybrids, the starting current draw should be much lower than any starter motor, so just triggering the booster and starting the car ASAP is probably the best thing to do as you don't need to build up that reservoir of energy to dump into a starter motor.

With those mahoosive jump starters it doesn't matter either way as they've more than enough current capacity to overcome any 12v sag  

[Minimac]

Hi I have recently purchased a RAV 4 2022 plate, Battery hybrid to replace my 12 year old Avensis that has been nothing but reliable. After 3 weeks and 400miles, driven everyday, we suddenly had a complete Battery fail, it was totally dead and recovery called, first time ever for a Toyota! We have been told the Battery needed recharging, and the dealer trickle charged it overnight, (not the dealer we bought it from as we were visiting Sussex, 250mile trip). They explained it could be because it had been sat before we bought it, that we should never leave it for more than 3 days without use as needs constant charging and as it does not have an alternator it is braking that charges the 12v battery so the long journey would not have charged it. I am now disappointed I chose this vehicle as owning it and relying on it do not look good. Is this typical of a RAV 4 and is there an indicator/ feature somewhere that notifys my of battery level. Am I always going to worry the battery will suddenly fail? 

 

[IanML]

That isn't quite correct.  Yes, it has no alternator, but the 12V auxiliary Battery is charged by the high-voltage traction Battery (through a dc-dc converter), which is charged by regenerative braking, and by the petrol engine when the car is "ON" (i.e in Ready Mode) if the charge drops below a certain level.

The chances are that either the auxiliary Battery or the dc-dc converter is defective.  If you have driven 400 miles in 3 weeks, it should be very well charged.  If the aux and traction batteries are both low, with the car in Ready Mode and stationary, the petrol engine should start, to charge them.

If you have "aux battery anxiety", you can fit a bluetooth monitor (e.g. ANCEL BM200), which will keep you informed via your mobile phone.  If you are not using the car much, a periodic charge with something like a CETEK MSX-5 will do the trick.  

[Minimac]

Thank you, that's useful to know, we were very surprised by the response given and that this is a common problem and we should need to always be charging the Battery ourselves. I will look into getting a monitor.

[ernieb]

I have a simple 12v monitor in the auxiliary socket (PHEV) and use this to keep an eye on the 12v when I start the car and during the trip.

This is not just a Toyota issue, many other manufacturers seem to have similar issues with HEV/EV’s small 12v Battery with lots of 12v essential systems calling for power when the car is started. 

[philip42h]

18 hours ago, Minimac said:

Thank you, that's useful to know, we were very surprised by the response given and that this is a common problem and we should need to always be charging the battery ourselves. I will look into getting a monitor.

It's really not a problem - as Ernie suggests, it is a feature of hybrids and EVs having more complex electrical systems and smaller auxiliary batteries. The vast majority of us drive around very happily without worrying about it at all. That said, it does help to be aware of it and avoid obvious pitfalls - like using Accessory mode for an extended period or leaving the car standing for many weeks. Anyone using their car for more than an hour per week / doing more than 2000 - 3000 miles pa won't need to think about it.

Did you leave the car in Accessory mode (to listen to the radio for example)? If not, it does sound as though your car may need a new auxiliary Battery ...

 

[IanML]

20 hours ago, IanML said:

  If you are not using the car much, a periodic charge with something like a CETEK MSX-5 will do the trick.  

Correction.  That should be CTEK MXS-5

Actually, the NOCO Genius 1 looks quite suitable and much less pricey.