Going away for a week's holiday - do I power off the MG4 completely?

Hallix73 said:

I got this from Ali Express, very useful and should do the trick.27.65￡ 30% OFF|New Arrival Car Jump Starter Power Bank Starting Device Diesel Petrol Car Battery Charger For Car Battery Booster Buster - Jump Starter - AliExpress

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Thanks for that I’ll have a look at that one. There is so much choice out there and wasn’t sure what to go for.

Hallix73 said:

I got this from Ali Express, very useful and should do the trick.27.65￡ 30% OFF|New Arrival Car Jump Starter Power Bank Starting Device Diesel Petrol Car Battery Charger For Car Battery Booster Buster - Jump Starter - AliExpress

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That actually specifies diesel or petrol cars. If it also works on EVs, why aren't they saying so? (Forgive my ignorance.)

Have you read the reviews of that product on Ali?? I’d run a mile from it!

Diggsy said:

Have you read the reviews of that product on Ali?? I’d run a mile from it!

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I haven’t had chance since I have got back home I have been out pressure washing the paving in the back garden.

Have a read, one stood out straight away, with an image of the device like this…



…lots and lots of positive reviews, but not sure I’d trust it looking at the above…

Diggsy said:

Have a read, one stood out straight away, with an image of the device like this…

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…lots and lots of positive reviews, but not sure I’d trust it looking at the abov

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Diggsy said:

Have you read the reviews of that product on Ali?? I’d run a mile from it!

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Just had a look now and at the second review down. It’s frightening and dangerous if that’s what happens. I think I’ll do some googling for customer reviews of starter packs and have a look at Amazon too.

Kentboy said:

What it says in the headline. I won't be using the MG4 for eight days or so. The dealer said in these circumstances you should do a complete power down. But I've learned to question everything I've heard. Normally I just hit park and leave it. Is a complete power down a good idea? I do know how to do it but I'm not sure what the difference is between that and the usual hit park and get out of the thing routine.

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Left my Trophy in the airport car park for 7 days on 45% and when I got back it was still on 45% and I had no problems getting moving.
This was in January with o/s temperatures of -3c to +5c
What I did like was that I could check it's status from the beach in Mallorca from my phone

This is a really important topic in general, not just for planned holidays. I'm the only person who drives my car, so if I got sick the car would be sitting in the garage unused until I got better. I wouldn't expect an ICE car to be unstartable after a week or two unless the battery was already well dodgy, and if there are potential problems with EVs I want to know.

In 2019 I went on a ten-week cruise with a friend. She came to my house and put her Polo in my garage, then we drove to Bristol in my Golf to board the ship. In January. I insisted that both cars were left as full of petrol as possible, in case of fuel shortages on our return. I also took a car-starter kit with me, which was a lead-acid battery I bought in Halfords to replace a similar one that had leaked and died. My car's battery was little more than a year old though, and it started up pretty well when we got back to Bristol in March, only needing the brakes worked a bit.

When we got back to my house, the first thing was that my friend's car wouldn't start due to a flat battery. So the battery pack was used after all, and the car started. Then when she drove off, one of her wheels wasn't turning as the brakes had bound (despite it being left with the handbrake off). That needed a call-out from the garage. I was vastly grateful none of that had happened to my car at the docks in Bristol.

I'm not that certain what the 12v battery actually does in an EV. Is it required for starting as it is in an ICE car? I wouldn't expect an ICE car to develop a flat battery when left for a few weeks unless the battery was dodgy, and these are all new cars.

Can someone explain to me why the 12v battery is needed here, what it does, and why we're worried that it might go flat in cars that are less than a year old?

I don't believe there is any need to do the infotainment 'power down' procedure. That simply disconnects the high voltage battery.

But if you lock the car the same thing happens. And the car goes into deep sleep after a couple of days anyway.

Leaving it for a couple of weeks should be no different to leaving an ICE vehicle for 2 weeks: the main battery will hold charge and the 12V should be fine, provided you haven't kept the car awake by constantly checking it with the app.

Could you elaborate on that last bit? Sorry to be so ignorant but I've only had the car a couple of weeks. What happens when you check the car with the app, and if that does drain something, will it all be replenished next time the car is driven?

I’m believe The HV battery tops up the 12v even when off. I’ve left mine for over 2 weeks with front and rear dash am, no problem. The car is fully powered off when locked.

Rolfe said:

Could you elaborate on that last bit? Sorry to be so ignorant but I've only had the car a couple of weeks. What happens when you check the car with the app, and if that does drain something, will it all be replenished next time the car is driven?

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Basically every time you check the car with the app, the car runs through a series of tests, which uses power from the 12v battery. A few of these per day should be fine, especially if you’re driving or charging it often enough, or at least putting it in READY mode, which lets the HV battery top up the 12v.

But if you’re checking it all the time without driving or charging the car you could drain the 12v battery to a level that won’t allow the car to start. At least that’s how I understand it anyway.

That's helpful information. I've been tempted to check it the last few days because of seeing whether the app is actually working or not (it told me the interior temperature of the car was 87C the other day!) but now I'll know to be careful.

I've never heard anyone say that EVs were any more prone than ICE cars to dying on you if you left them parked up for a while, and given the amount of anti-EV propaganda out there I'd have thought someone would have mentioned it.

Rolfe said:

That's helpful information. I've been tempted to check it the last few days because of seeing whether the app is actually working or not (it told me the interior temperature of the car was 87C the other day!) but now I'll know to be careful.

I've never heard anyone say that EVs were any more prone than ICE cars to dying on you if you left them parked up for a while, and given the amount of anti-EV propaganda out there I'd have thought someone would have mentioned it.

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Whenever you check it a few times in the same day when it hasn’t been driven or charged, check the 12v battery status, which you can see on the ‘Vehicle Status’ screen. From what I can gather, it’s best to see that at 12.3v or above.

I usually keep an eye on it. I'm just not used to the idea that a lead-acid battery is something to worry about in a new car. But then, I never used my ICE car's battery to find out its status when it was parked, either!

Rolfe said:

I usually keep an eye on it. I'm just not used to the idea that a lead-acid battery is something to worry about in a new car. But then, I never used my ICE car's battery to find out its status when it was parked, either!

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Yep, I think that’s likely the biggest difference to be honest

I do remember flattening a battery by sitting talking in the car without remembering to switch off the lights. And even without lights on, I've tended to worry a bit about sitting in the car listening to the radio with the engine off. I think I did assume that since you're sitting on this huge high-voltage battery sparking with power then a battery going flat wasn't on the radar, but if the 12v doesn't charge up unless the car is running or charging, I see the problem.

I understand the advice about letting the car just go to sleep. I notice my Kindle does that. If I just put it down for a minute it wakes up again immediately, but if I haven't been using it for hours it takes a lot longer to boot up. I presume the cars are like that, but on a longer time-scale?

Rolfe said:

Could you elaborate on that last bit? Sorry to be so ignorant but I've only had the car a couple of weeks. What happens when you check the car with the app, and if that does drain something, will it all be replenished next time the car is driven?

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The car won't go into a deep sleep if you keep checking on it with the app - eg every day. So I have been told. I presume this could then affect its ability to snore gently and be ready when you return (ie I presume deep sleep is a very low power state minimising drain of either battery).

I'm catching on to that now, thank you so much.

Rolfe said:

That actually specifies diesel or petrol cars. If it also works on EVs, why aren't they saying so? (Forgive my ignorance.)

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I understand the 12v Battery is only used to power up the main console and hence open the software and screens so other main systems can be activated. When others have had problems with 12v flat battery the AA have just jumped charged with another 12V battery to get the car to wake up. Once its energised the car is good to go.
An ICE car requires a lot of starting current from the battery to overcome the friction and momentum to turn the engine over so the poissible burn outs in reviews may be on starting a large engine. However EV's dont have high torque starter motors and like I say the 12v battery is just mainly to get the cars main systems activated.
I have used the one I got to start my Triumph Stag 3.0 litre V8 and was fine.