12v battery discharge

[Shawwzy]

My 12v Auxiliary Battery has let me down on 5 occasions now. I am getting to grips with it now and I am trying to work out if it is my fault or a design fault on Toyota’s part. It is very frustrating but so easy to remedy by charging the Battery. Anyway, the last occurrence happened after I plugged in early evening to get an overnight charge which did not happen. My charging door was open and connector plugged in for 11 hrs. It states in the drivers manual on page 32 that you should avoid this. The charger I have is complete rubbish and wholly useless and completely unreliable. Please under no circumstances buy a WALLBOX max, you will be leaving yourself open for hours and hours of frustration and disappointment.

[philip42h]

Quite so ... page 83 in my Owner's Manual states:

Quote

● To prevent the 12-volt battery from being discharged, do not leave the charging port lid open or the charging cable connected to the vehicle.

It feels quite bizarre to have the Owner's Manual but not the car, nevertheless, does anyone know why this should be so? Does simply having "the charging port lid open" drain the 12V auxiliary Battery? Why?

 

 

[Cyker]

One *really stupid* thing I've seen with with a lot of EVs is the 12v Battery does NOT get charged when the traction Battery is being charged by AC (More will when DC charging), but the 12v still has to run the computers to allow the charging to take place.

I don't understand why so many manufacturers made this design choice as it makes zero sense. It may be the bz also has this bizarre design flaw...?

[philip42h]

55 minutes ago, Cyker said:

One *really stupid* thing I've seen with with a lot of EVs is the 12v battery does NOT get charged when the traction battery is being charged by AC (More will when DC charging), but the 12v still has to run the computers to allow the charging to take place.

I don't understand why so many manufacturers made this design choice as it makes zero sense. It may be the bz also has this bizarre design flaw...?

 

Quote

■ Charging the 12-volt battery.

The 12-volt battery is charged from the traction battery when the EV system is operated or while the traction battery is being charged.

I did say that I had the Owner's Manual ... 😉 

[leosayer]

1. I have had the car 20 months now and i never had the 12v falure

2. Are you suggesting avoiding overnight charges but prefer short frequent charges?

3.in the unlikely event the 12v Battery fails and i use a jump starter do you advise that I should then take it to the dealer for a change of Battery?

[philip42h]

14 hours ago, leosayer said:

1. I have had the car 20 months now and i never had the 12v falure

2. Are you suggesting avoiding overnight charges but prefer short frequent charges?

3.in the unlikely event the 12v battery fails and i use a jump starter do you advise that I should then take it to the dealer for a change of battery?

1. I've had my RAV4.5 for over four years without any 12V system issues - the hybrids and EV share the same 12V system 'weakness'. It's really not a problem, but it helps if the owner is aware of the potential issue and what to do / not to do. @Shawwzy's post helpfully highlights a characteristic of the bZ4X.
2. I don't see any reason to avoid overnight charges - the thing to avoid is having the charge door open for an extended period when the car is not on charge. If your schedule includes charging between midnight and five am (say) then the12V auxiliary Battery will be fully charged by the end on the charging session. The issue arises when the scheduled charging fails to happen.
3. Lead acid batteries are designed to be rechargeable. If you merely run it down and need to use a jump starter / recharge the 12V auxiliary Battery explicitly on the odd occasion, no harm is done - no need to change the battery. If you totally flatten the 12V Battery on multiple occasion such that it will no longer accept / hold charge as specified it would then be time to replace that battery. Note that the 12V auxiliary battery is an expendable item needing replacement (normally after 5-10 years).

The best charging strategy for you will depend on your individual use and journey profile. If you don't need to do more than 100 miles each day, then waiting to charge the car until it drops to around 50% SoC and then charging to 100% during the off-peak period would probably work well both in terms of energy costs and the "charge door open but not charging" issue ... maybe?

[leosayer]

Dear Philip thanks for your comments I ill agree entirely on all points except for charging to 100%. I usually charge it to 80% occasionaly charge it to 90% and only once to 100%

[philip42h]

14 hours ago, leosayer said:

Dear Philip thanks for your comments I ill agree entirely on all points except for charging to 100%. I usually charge it to 80% occasionaly charge it to 90% and only once to 100%

This thread was about the 12V auxiliary Battery, so, allowing a little topic drift, why don't you charge to 100%?

• There's nothing in our owner's manuals to suggest that we shouldn't.
• Toyota limit the useable capacity to 90% of the theoretical capacity by design. So what we see as 100% is around 64 kWh - approx 90% of the 71.4 kWh label on the tin.
• We know that very frequent rapid DC charging may shorten Battery life, and that in terms of journey time it is more efficient to charge to around 80% and move on than to continue to 'hog' the rapid charger to take on a little bit more. Above around 80% rapid chargers aren't rapid any more.

There's no guidance given by Toyota NOT to charge to 100% using a slow or fast AC charger.

But there is a lot of FUD on the Interweb ... 😉

[wivenhoe]

There is nothing in the Battery warranty about degradation not being covered if the Battery is always charged to 100%. If AC charging to 100% was to degrade the Battery then I’m sure Toyota or Lexus would get the software to limit charging like that. I’m not sure about the BZ, but the RZ will not allow 3 rapid charges in 24 hours - it limits the speed on the 3rd charge so I’m sure a similar ‘protection’ would apply for going to 100%. As Philip says, it’s a 100% of what ?