CHR Battery resting voltage

[Hibird]

My vehicle is fitted with an original AGM Battery & Victron BT Battery voltage monitor (other makes are available of course). This vehicle is used on a regular basis and has spent 2 weeks twice in the last year in airport car parks and has never suffered any kind of flat Battery issues. The monitor adds an additional 2ma to the vehicle quiescent current loading so can almost be ignored.

Having the battery voltage monitored by BT is not only convenient but also allows a true reading of a resting battery voltage of a locked secured vehicle with a fully stabilized battery voltage.

When the car is in normal use (being driven or in ready mode) the voltage at the battery terminal via the BT monitor varies between around 13.6V - 14.8V which is clearly down to whatever the Toyota charging algorthm decides based on many factors and probably quite complex and in part to maximise fuel economy.

There are often posts about flat batteries and some about flat batteries being replaced only to go flat again. There seems to be some sort of acceptance that flat batteries is the Toyata Hybrid way of life and of course that is the case for any modern vehicle not used for extended periods of time but the periods often reported here are far from extended.

So now to the interesting part my vehicle typically shows a battery voltage of 12.4V after a 24 hour period of rest and while I suffer no flat battery issues this voltage seems lower than ideal to me. A reading of 12.6V would be a better number which would represent around 80% charge by my reckoning. Perhaps any folk that suffer from flat batteries that have recorded any similar data would like to comment.

There are many reasons for a flat battery but this post is looking specifically at if the battery is actually getting fully charged in the first place.

 

 

 

[philip42h]

To add ...

The 12v auxiliary batteries fitted in the Japanese made RAV4s are maintenance free, wet (flooded) cell batteries complete with inspection port and unscrewable caps so that you can add electrolyte. The OEM batteries are Yuasa - if I try to get a replacement in the UK Yuasa offer an AGM equivalent. So, I suspect, the type of OEM fitment will depend on where the Toyota is manufactured.

As I understand the quiescent current must be less than 50mA - hopefully it is no more than 30mA. So, the additional 2mA draw of a BT voltage monitor isn't entirely negligible. But, as you say, it is convenient ...

Do you ever see the voltage below 13.6v in Ready mode? If not, it suggests that Toyota has chosen to run the '12v' circuit at 13.6v (and boosts that to 14.8v only when they have decided that the auxiliary Battery needs charging). That all seems reasonable to me ...

Now, you say that you Battery shows 12.4v after a period of quiescence of 24 hours - this too seems perfectly reasonable to me; I wouldn't really expect more. You might well expect to see 12.6v - 12.8v if you were to measure the voltage 'open circuit' - i.e. with nothing connected and no current draw. But that isn't the case here - the Battery is in circuit with a draw of somewhere between 30mA and 50mA (probably).

And finally you ask "if the battery is actually getting fully charged in the first place" - probably not, 95% will probably do for all practical purposes. There's no starter motor to turn so maximum CCA are not required. And the battery is inside the car (well, the boot space) so Toyota would probably choose to marginally undercharge the battery than risk overcharging and any potential gassing that might occur.

Just thoughts ...

[Trewithy]

I am no expert and the following is purely anecdotal but I have been told that to charge the Battery faster turn on the headlights whilst driving.  Apparently the car detects a drain on the Battery and forces the car to recharge the Battery at the highest rate.

[Cyker]

I've heard similar things for the headlamps and also AC, but never found out if they were true or not!

 

[Derek.w]

It works on any car with a alternator increase load to charge up drained Battery faster.

I also noted it works on my hybrid as Battery drain is less for the same jurney but have not taken any readings to prove it.

[Dala]

I confirm - I measured
when driving with lights, the charging voltage is 14.2V - 14.4V
when driving without the lights on, the voltage is reduced to 12.8V-13V after 20-30 minutes of driving (without heating the seats, windows, etc.)
 

[Hibird]

I am pretty sure the lights on/off v's charging volts is the sytem working as it should do and makes perfect sense. However the real question is the Battery being fully charged or at least being charged to a level that gives maximum help for the flat Battery guys and best service life for the regular users not having an issue like me.

As stated I reckon my 12v Battery probably lives at arounf 80% SOC. I do not have any data that tells me what effect 90% SOC may or may not have on battery service life although my best guess would be very little if any but I may be wrong. However 90% + SOC may help the flat battery guys by giving a bit more of a buffer before the slow death creeps in.

Doe anyone have any opinions/data that would suggest their battery SOC is significantly different to my 80% and if they have battery issues or not.

[TonyHSD]

No Battery issues to date. I had never monitored the soc of 12v Battery but had measurements done when the car is not in use after few days left in the cold last lockdown and was around 12.24v . When the car is ON the charging voltage been 14.8 or even 15v as seen by the ecu , measurements  shown on Carista app. 

[Hibird]

I am unsure what type of Battery is fitted in TonyHSD vehicle but if it was an AGM 12.24V and the measurements were made with the Battery connected and stabilized this would represent a SOC of around 40%.

I would class that as pretty low and well into the needs a recharge soon band. If this measurement was taken Open circuit the I guess SOC was around 60%.

Of course I don't know what the SOC was before the 'few days' of no use but assuming it was reasonable those few days took there toll. But I think this vehicle gets a lot of use from the annual milages posted by Tony so his exposure to damage is low... like very low. I would be surprised if a car whith such impressive annual milages was a candidate for Battery problems.

Intrersting info thanks Tony

[Hibird]

I carried out some measurements of the total energy required to bring the 12v Battery up to a fully charged condition after what I am confident is a full charge from the vehicle system and an overnight rest period.

I would have to conclude that my Battery is receiving a more than adequate charge from the onboard charging system and even allowing for uncertainties arrive at SOC number of above 90% which seems reasonable to me.

I plan no further work as it's all good here.

If you have found anything different please share

[TonyHSD]

On 12/31/2022 at 1:51 PM, Hibird said:

I am unsure what type of battery is fitted in TonyHSD vehicle but if it was an AGM 12.24V and the measurements were made with the battery connected and stabilized this would represent a SOC of around 40%.

I would class that as pretty low and well into the needs a recharge soon band. If this measurement was taken Open circuit the I guess SOC was around 60%.

Of course I don't know what the SOC was before the 'few days' of no use but assuming it was reasonable those few days took there toll. But I think this vehicle gets a lot of use from the annual milages posted by Tony so his exposure to damage is low... like very low. I would be surprised if a car whith such impressive annual milages was a candidate for battery problems.

Intrersting info thanks Tony

You are welcome. 
A bit late reply, sorry for that I had missed to read your posts. 
I had measured my Battery straight after unlocking the car and removing the cards around the boot where Battery is located and the interior lights been ON for few minutes. Before that the car was not in use for 2 days - 48 hrs inactive. But you are right, when I drive I do a lot, 12hrs a night from which will be driven at least 6 hrs and in colder weather like now another 2-4 hrs in ready mode for heating and electric power for my devices. I also go holidays every 6 months for a week and I had no problems to report. 12.5 years , mileage to date 239k., all original batteries., if the Battery by any chance been replaced by the previous owners still respectful life of 7.5 years and 200k miles. Let see for how long more will last. 

[Gray86]

We are doing a bit of a test with my Dad’s 2.0 CHR currently. He charged it 3 weeks ago on his CTEK charger, used it for local trips once or twice, and left it locked (Alarm on) in the garage for the last 2.5 weeks whilst on holiday. Will see if it’s flat when he returns tomorrow. I expect it’s just fine. . . 

[Hibird]

12 hours ago, Gray86 said:

We are doing a bit of a test with my Dad’s 2.0 CHR currently. He charged it 3 weeks ago on his CTEK charger, used it for local trips once or twice, and left it locked (Alarm on) in the garage for the last 2.5 weeks whilst on holiday. Will see if it’s flat when he returns tomorrow. I expect it’s just fine. . . 

Look forward to your findings, my CHR has just spent it's third 2 week airport parking event without issue.

[Roy124]

Monitoring my Yaris Cross, it looks like the voltage drop is miniscule when the car is static and not doing anything.  

Yesterday I opened a rear door couple of times and later locked the car using the App.  Each event caused a ripple on the voltage.  One, I think door opening, showed a 0.5 drop to below 12v before recovery to 12.36v. 

[Dala]

According to available information, it seems that the car Battery voltage will stabilize at 12.3V-12.4V.  Then it drops.  According to car Battery manufacturers, sulfation will already occur.  I'm confused.

[GBgraham]

On 12/30/2022 at 4:28 PM, Hibird said:

My vehicle is fitted with an original AGM battery & Victron BT battery voltage monitor (other makes are available of course). This vehicle is used on a regular basis and has spent 2 weeks twice in the last year in airport car parks and has never suffered any kind of flat battery issues. The monitor adds an additional 2ma to the vehicle quiescent current loading so can almost be ignored.

Having the battery voltage monitored by BT is not only convenient but also allows a true reading of a resting battery voltage of a locked secured vehicle with a fully stabilized battery voltage.

 

Not sure which model but I cannot reason why you would fit a Victron Battery monitor to your car especially having to use it in conjunction with a shunt. 

As mentioned, an open circuit of a healthy Battery should show 12.8v. All modern cars have permanent discharge of varying degree and again as stated, on average around 50ma.

Most charging systems operate at 14.8v under no load, there are some a tad higher or lower but when you switch loads on the alternator will produce more amps, hence the voltage comes down, (refer to Ohm's Law)

To keep your Battery healthy, daily use is sufficient, occasionally a week or even a fortnight unused and the charging system can easily cope to replenish but to regularly leave for long periods does effect the long term health of the battery under these circumstances.

It's always good to use a trickle or some electronic charger like the CTEK to keep a battery healthy on a car that is not used so often as the car charging system may only produce around 95% of it's charge if the battery has been seriously discharged.

The worst thing for any battery is to be left discharged or constant discharge cycles will shorten it's life.

These are all general assumptions and not attached to any one particular vehicle

[Hibird]

It was a BT Battery voltage monitor & of course did not include any shunts !

[Hibird]

Like this

[GBgraham]

4 hours ago, Hibird said:

Like this

A cheapo voltmeter will tell you all that you need to know, so sorry but there is no silver bullet for Battery problems as the parameters are so great.

[Hibird]

17 hours ago, GBgraham said:

A cheapo voltmeter will tell you all that you need to know, so sorry but there is no silver bullet for battery problems as the parameters are so great.

It's a bluetooth voltmeter Graham it takes voltage readings, it does not cure or fix any problems and makes no silver bullit claims. I don't have a cheapo voltmeter to compare it with but stands up well against a couple of Fluke meters !

I have no problems requiring special vampire elimination ammunition, ohms law or batteries but enjoy your cheapo meter !

[Gray86]

On 3/24/2023 at 8:14 PM, Gray86 said:

We are doing a bit of a test with my Dad’s 2.0 CHR currently. He charged it 3 weeks ago on his CTEK charger, used it for local trips once or twice, and left it locked (Alarm on) in the garage for the last 2.5 weeks whilst on holiday. Will see if it’s flat when he returns tomorrow. I expect it’s just fine. . . 

It was fine, although when stuck back on the CTEK after 3 weeks the charger stayed on 2 for a good while, indicating that the Battery was quite low.  Perhaps 4 weeks left idle on a fully charged Battery is possible at a push (with a few days of sub-zero temps), but that’s your lot 

[Dala]

Did you measure the car Battery voltage before connecting the charger?

[Gray86]

On 3/30/2023 at 8:49 PM, Dala said:

Did you measure the car battery voltage before connecting the charger?

No, don’t have the tools to do that - could only rely on the charger settings to understand some approximation of Battery level