12volt battery low on MG3 Hybrid Trophy

Radish

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MG3 Hybrid+ Trophy
I purchased an MG3 hybrid Trophy in July 2024, it has been fine since then but the last few weeks it shows 12V battery low when ignition switched on. I have contacted the dealership for an answer and am still waiting to hear. Anyone else had this problem and been given an answer ?
 
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I've not had any issue with the 12volt battery. It is a recorded issue with the Toyota Yaris mk4, when owners leave it sitting up for a few days, but I haven't heard of any issues on this forum. Have you had the battery tested? Have you hard wired a dascam or similar?
 
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I've not had any issue with the 12volt battery. It is a recorded issue with the Toyota Yaris mk4, when owners leave it sitting up for a few days, but I haven't heard of any issues on this forum. Have you had the battery tested? Have you hard wired a dascam or similar?
I have a dash cam but it is plugged into to usb socket behind the rear view mirror and is only live when the ignition is on.
 
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I purchased an MG3 hybrid Trophy in July 2024, it has been fine since then but the last few weeks it shows 12V battery low when ignition switched on. I have contacted the dealership for an answer and am still waiting to hear. Anyone else had this problem and been given an answer ?
Had major problem this week - returned to station car park to find my lights were on and car unlocked but no power - called MG recovery and after a couple of hours someone arrived at boosted the 12V battery - an electric car left beside me during g that time of waiting for help. Early in the morning I locked my car and the headlights were not on went I went off by train. It was 13 hours later that I returned. The dealer felt that the electric car beside me had a similar frequency on its keypad and after I parked the person arrived later - locked her car and set off a sensor on my MG putting the headlights on !! I got home ok but many apps said parts of my MG were not working - after plugging up for charge they returned to normal. Dealer said to charge up 12V battery which I did - it was registering about three quarters full. MG recovery not very helpful - said my cover had finished when the car was a year old - but dealer says it automatically renews after each MG service !!
 
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dealer says it automatically renews after each MG service !!
I thought same sure dealer mentioned it as a benefit getting service through them. Just searched and it says it on MG service page as well.
 
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I purchased an MG3 hybrid Trophy in July 2024, it has been fine since then but the last few weeks it shows 12V battery low when ignition switched on. I have contacted the dealership for an answer and am still waiting to hear. Anyone else had this problem and been given an answer ?
Yes. Called dealership. Arranged a battery check
 
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Hi
Get a 12V charger from a car shop and charge up the battery using this and if it doesn’t hold a charge then it needs to be replaced.
 
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Has anybody discovered the 12V battery voltage indicated on the dash does not agree with their voltmeter? The car had not been used for 4 weeks so was surprised when dash indicated 14.1V and my meter read 12.3V - not a very reliable reading is it!
 
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was surprised when dash indicated 14.1V and my meter read 12.3V - not a very reliable reading is it!
It may be 14.1 V at the battery terminals, where I believe the measurement is taken. You possibly read the voltage from the 12 V outlet or the OBD-II port, which may be after a fuse, thin wiring, and with other loads.

That's still a big difference though. Is your multimeter trustable?
 
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That's right we must assume the dash voltage is taken at the battery terminals - as was my meter reading.
It's a new meter and makes perfect sense voltage-wise on our other car batteries.
It appears MG's idea of this voltage may not be trusted.
My dash reading was noted after simply switching the car (cold) on, engine not running and the meter reading taken immediately after. Might just need to be mentioned at that first service coming up...
 
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Note it was first thing in the morning, the engine was not running so not being charged and yes agree the battery is down. We had recently been away so it might be expected.
Has anybody else found an error here?
 
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14.1V is the voltage from the alternator not the battery.
Does the hybrid drive-train actually use an alternator driven by a fan belt? That seems so clumsy when you could run a DC-DC from the hybrid battery. Also, the engine is not running at all for potentially long periods of time.
 
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Sorry too used to ICEs. Then it will be from the battery management system using the HV battery to charge the 12V I guess.
14.1V is the "standard" max used from an alternator & I presume that is carried over to EVs.
It doesn't mean the 12V battery has 14.1V. Rather that it is being recharged and full power and or you have a lot of ancillaries running.
 
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I believe the 12V battery is charged via a dc/dc converter from the high voltage battery.
This prompts the thought the battery dash voltage is only shown with the car switched on - so are the main batteries then charging the 12V one?
I tested the 12V battery with the power all off...
 
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