12v battery maintenance

[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]

7 hours ago, 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