Replacement 12V auxiliary battery for MGS5

[davemoore59]

I have setup a card in Home Assistant to monitor my S5:

As you can see it does monitor the Aux battery (voltage) so the data is available?

 

[Unlinked]

I have setup a card in Home Assistant to monitor my S5:
View attachment 43277
As you can see it does monitor the Aux battery (voltage) so the data is available?

how do you do this? I am familiar with HA, not an expert but I imagine you need HACS and your card may be custom

 

[davemoore59]

how do you do this? I am familiar with HA, not an expert but I imagine you need HACS and your card may be custom

Yes exactly that - the setup involves a 2nd user for the MG app logon (as only one logon per user at once) and chat gpt walked me through the steps AND suggested the card to use and it worked a treat (obviously you can choose what info you want to display)

 

[Joningy]

Brilliant news on my S5 12v auxiliary battery, after being sat at Gatwick airport for three and a half weeks and my previous experiences of it going totally flat.

Despite my fears, it survived and started the car perfectly on our return last night 17th Feb.

I've now got restored confidence in my MGS5, all the hassle was down to fitting permanent live a dash cam, sounded a good idea at the time, but thinking about it, the number of times a car is going to get a bump whilst parked and asleep must be pretty minimal.

So this is a warning to all thinking of being a smart arse like me, fitting a dash cam with permanent live monitoring, the puny 35Ah12v battery cant cope with any more than a few days idle without causing grief and flattening the battery.

BTW my dash cam is a Viofo A229 Plus, other brands may not draw as much standby current, it would be interesting to know if others have similar problems with their dash cams.

 

[MG Clive]

Great news @Joningy.

 

[marcbesty]

My issue was that the gateway module was staying awake and draining the 12v battery. Let's see if I have anymore issues over the next few weeks

 

[T1 Terry]

My issue was that the gateway module was staying awake and draining the 12v battery. Let's see if I have anymore issues over the next few weeks

That follows on with the theory the phone being so far away from the vehicle, Bluetooth couldn't keep waking it up .....

T1 Terry

 

[giantbike66]

So this is a warning to all thinking of being a smart arse like me, fitting a dash cam with permanent live monitoring, the puny 35Ah12v battery cant cope with any more than a few days idle without causing grief and flattening the battery.

I have successfully installed the Blackvue front and back dashcam connecting to a external Blackvue battery (see photos) which is connected to the 12V cigarette plug permanently in the middle compartment. Contrary to popular belief, this outlet isn't permanently on, as I have the Blackvue battery app that confirmed the supply is off as soon as the car is off. I had this system connected this way for couple of months now, and I have never depleted the external 12V battery. The only catch is to fit a toggle switch between the camera and battery, so as soon as I'm home I can turn off the camera system. Otherwise it will deplete the Blackvue battery overnight. This battery system can maintain the camera in recording mode whenever I'm out and about for security purposes.

 

[Joningy]

That is interesting and a bit risky if you forget to toggle the dash cam off @giantbike66 , but I reckon nowhere near as bad as draining the 112v auxiliary battery.

But I wonder why you went that route to power up the device and didn't use the 12v USB A dash cam socket to the left side of the rear view mirror cluster, it's a switched supply and not permanent live, unless of course it isn't available on Australian S5's !!!

Inside info required @T1 Terry

 

[LaS]

As you already know? The 12v battery should never drain/discharge/go empty due to the "intelligent charging" function. But as many included my self have experienced this does NOT work.

 

[giantbike66]

That is interesting and a bit risky if you forget to toggle the dash cam off @giantbike66 , but I reckon nowhere near as bad as draining the 112v auxiliary battery.

But I wonder why you went that route to power up the device and didn't use the 12v USB A dash cam socket to the left side of the rear view mirror cluster, it's a switched supply and not permanent live, unless of course it isn't available on Australian S5's !!!

Inside info required @T1 Terry

Yes, the Australian model do have the USB plug near the rear view mirror. However, the external battery pack I have ( BlackVue B-124X Power Magic Ultra Battery for Extended Parking Mode Operation and Recording : Amazon.com.au: Automotive BlackVue B-124X Power Magic Ultra Battery for Extended Parking Mode Operation and Recording : Amazon.com.au: Automotive ) comes with cigarette lighter plug. And the car's cigarette socket is nearby, so it's the easiest way to connect

If I happen to leave the camera on after home, worse case scenario is the depletion of this battery pack overnight, which I have done numerous times this couple of months. But as soon as I start driving, the battery pack will be topped up whilst driving. Only thing it takes more than half an hour of driving to top it back up. So I try to turn off whenever possible. Despite the specifications claim of over 24hours of parking recording capacity, I find it only capable of no more than 5 to 6 hours if lucky. The good thing is, it does provide some comfort in knowing, there will be recorded footage if some things happen to the car while I'm off somewhere

 

[nem]

Jumping in here with my experience.
I recently broke my tibia and fibula so car was parked for 3 full weeks in temps ranging from -5 to -15c. SoC on HV was about 42%.

I was worried that it would be completely dead after this but there was no problem starting and driving it. I've had a mate over regularly now, driving the car for a bit to make sure it stays that way.
It's getting a bit warmer now tho, so it should be fine going forward.

Just my experience so far!

 

[stevedee]

Our S5 was parked in the drive early in February. It hasn't been touched since, and we haven't run iSmart to check that 'baby' is OK!

Now we are back! And its no surprise that our S5 is absolutely OK, after 26 days of complete inactivity.
The 12V system battery has been charged periodically from the HV (traction) battery as expected.
The only small surprise is just how little energy was required to maintain vital systems on the car during this period. Our S5 went into a deep-sleep state, and we did nothing to wake it during this time.

Some numbers:
HV battery SoC at start: 79.9%
...after 26 days: 78.9%

Estimated power per %SoC: ~62kWhr for 100%, so 620Whr for 1%

Conclusion: all things being equal, our S5 could be left for a very, very long time (i.e. months, possibly years) before the 12V and HV batteries would go flat.

Comments:-

That "puny" 12Volt battery?
I don't think so. The 12V system battery on the S5 is just a small 'energy reservoir'.
Unlike the battery on a non-ev, it doesn't have to spin up (crank) the engine to get it started.
It only has to provide power for some low power I/O, telemetry, a stable 5Volt USB supply for peripherals, & a low voltage supply for processor & other digital electronics.

Dash-cam wiring
It seems to me that you could use an 'always on' dash-cam without the risk of draining the battery, since the camera input power is unlikely to be much more than 1Watt.
But when I get some time I will: a) measure current drawn by our dash-cam, & b) wire a suitable dummy load across the 12V battery and check that the system can still cope.

EV vs non-EV
I wonder what would happen if you left a 2025 model non-EV car, with similar electronics, for 26 days?
Just like the S5, it would still have to maintain vital functions such as: electronic door monitoring, the anti-theft system, telemetry & so on.
What is the rating for a typical FLA battery fitted in modern petrol engines? I can't imagine the battery on such a car would last much longer than a few weeks.

"Parasitic Paranoia"
Don't worry about what might be draining your 12V system battery.
Its better to ask the question: "Why is my car not maintaining the 12V battery, while the HV battery has sufficient charge?"
An EV that would allow the 12V system battery to go 'flat', while there is a huge power reserve in the HV battery, would surely be a crap design.

Our MG S5ev is not crap!

 

[asandrews]

Sometimes I will park up and sit in the car for a while (say my wife is popping in a shop). If I leave the radio on and turn off the car, after just a few minutes it will say 'the 12V battery is low. Turning off in x seconds'.

Does anyone else have it last just a few minutes?

I have left it untouched for a couple of week whilst on holiday before with no issues at all, so it feels like an over-reaction to me.

 

[Ian Key]

Sometimes I will park up and sit in the car for a while (say my wife is popping in a shop). If I leave the radio on and turn off the car, after just a few minutes it will say 'the 12V battery is low. Turning off in x seconds'.

Does anyone else have it last just a few minutes?

I have left it untouched for a couple of week whilst on holiday before with no issues at all, so it feels like an over-reaction to me.

You don't need to turn the car off, and yes it could be an over reaction, but it's better than the alternative.

 

[emmrecs]

Sometimes I will park up and sit in the car for a while (say my wife is popping in a shop). If I leave the radio on and turn off the car, after just a few minutes it will say 'the 12V battery is low. Turning off in x seconds'.

Does anyone else have it last just a few minutes?

Yes, quite regularly in the sort of scenario you're describing.