MG5 12v Battery Replacement Cost?

[HoriUK]

Evening all. Looks like this cold weather has done for our 12v battery - after a week of the infotainment playing up, today the car was totally dead.

Our neighbour kindly (especially as the AA aren't responding to homestarts today) gave us a jump, and when it came back to life I think it went though every warning it's got! Annoying, as when I looked yesterday it was reading 14.5v (now 13.7v).

Anyway, as our car is now a whopping 14 months old it looks like we'll have to cough up for a replacement - anyone know how much the dealers charge for one, or what regular battery size fits? Cheers.

 

[Elec Car Aust]

Evening all. Looks like this cold weather has done for our 12v battery - after a week of the infotainment playing up, today the car was totally dead.

Our neighbour kindly (especially as the AA aren't responding to homestarts today) gave us a jump, and when it came back to life I think it went though every warning it's got! Annoying, as when I looked yesterday it was reading 14.5v (now 13.7v).

Anyway, as our car is now a whopping 14 months old it looks like we'll have to cough up for a replacement - anyone know how much the dealers charge for one, or what regular battery size fits? Cheers.

View attachment 13783

Side issue from your questions. Buy a small lithium jump starter and keep in the boot. They are light, cheap and fit in palm of your hand and are Lifesavers when you need a jump start.

 

[Gomev]

My 12v battery died too in the cold weather, but seems to have been resurrected somewhat now that it's warmed up. Now I no longer trust it not to do it again though, so have bought a replacement size 75 battery from Tayna.

If you press the Start button twice without pressing the brake, the display will show the charge in the 12v battery; if you press the Start button and the brake pedal (ie Ready mode) it will show you the charging voltage (hopefully between 13v and 14v). NB it only charges the 12v battery from the HV battery when in Ready mode, so if you try to warm up the car without having started with the brake depressed, then it will drain the 12v battery, which is not ideal!

Dealer wanted £75 + VAT to order one for me (or £110 + VAT fitted).

Not sure if it needs to be continuously connected to a 12v source to preserve codes etc when ing the battery?

Welcome to the forum @Smudger

 

[Tim Falkiner]

I have an MG ZS EV Mk1 in Melbourne and the 12 v battery started playing up at around 12 months. It just seems to be on the way out with readings of around 12 volts. The dealer has checked it out and says it is ok but I doubt it will last once the weather gets colder. Makes sense to trickle charge occasionally and carry a jump starter. One rumour is that when MG set up the 12v charging for the Mk 1 it used the same charge settings as for the petrol car without factoring in that 12v batteries in EVs can be used to run the air conditioning when the car is not being driven. It may also be that deep charge batteries are better suited to EVs. Another possibility is that the battery went flat whilst the car was being shipped from China.

 

[BugEyed]

Not sure if it needs to be continuously connected to a 12v source to preserve codes etc when ing the battery?

It doesn't. Nothing is lost by disconnecting the 12v even for an extended period provided you were not updating any code at the time. £35+VAT for fitting is extreme. Frankly Halfords would be cheaper if you don't want to DIY, and they'll come to you as will both the AA and RAC.

 

[Jto]

Just a update, my car has not moved or been charged since Christmas Eve. The battery reading on the screen was 10 volts, I have moved it across the drive and the battery came up to 11 volts but not sit there for five minutes to let the battery settle. I have now plugged in the car to charge tonight and will let you know what the voltage is tomorrrw.

 

[Alb]

If accurate, 10V would mean the battery was fully discharged.

 

[BugEyed]

Agreed. Don't leave it at that level as it will damage it. You need to leave the car switched on for at least an hour. Ideally lock it using the emergency key and keep the other key well away from the car and it'll be safe.

 

[Deep purple]

Another problem with a fully discharged battery, apart from the damage it does to the battery, is that it can freeze at about -10C.
A fully charged battery with no load has a voltage of about 12.8-9 (dependant on temperature). The challenge with EVs, as a lot of drivers of all makes have probably found out through experience, is that the 12volt battery is only charged/supported by the main HV battery when the car is in RUN mode and the HV battery is connected. In other modes all the parasitic loads, which in an EV are higher than ICE cars, are being fed from the 12 volt battery alone. So sitting in the car not in RUN mode but with all the services on you will drain the 12 V battery quickly. Just watch the voltage dropping!
The suggestion that EVs should have deep cycle batteries is a very interesting one as there is no requirement for high cranking currents but there are likely to be a lot more and deeper cycles than in an ICE car.
There has been a lot of discussion about using nominal 12 volt Lithium batteries in EVs but no major shift yet for a variety of reasons.

 

[Jto]

Hello
charged the car last night for around two hours, meter reads just under 12v I do not think the meter is very accurate so it only there to give you a guild. I do a lot of short journeys in the week not many long in the year, I feel just like ICE lot of short journey the battery will not get a full charge back into the battery when you have lights heater running. I would suggest in the colder weather is to put your EV cars on charge each night and top them back up to 80% or 100% depending on the type of HV battery.
Also doing a trickle charge would be a good idea as suggested in a post on here.

 

[Lovemyev]

Our ZS LR has not been used from the 22.12.2022.
Here is the state of the 12 volt battery.

 

[Gomev]

Another problem with a fully discharged battery, apart from the damage it does to the battery, is that it can freeze at about -10C.
A fully charged battery with no load has a voltage of about 12.8-9 (dependant on temperature). The challenge with EVs, as a lot of drivers of all makes have probably found out through experience, is that the 12volt battery is only charged/supported by the main HV battery when the car is in RUN mode and the HV battery is connected. In other modes all the parasitic loads, which in an EV are higher than ICE cars, are being fed from the 12 volt battery alone. So sitting in the car not in RUN mode but with all the services on you will drain the 12 V battery quickly. Just watch the voltage dropping!
The suggestion that EVs should have deep cycle batteries is a very interesting one as there is no requirement for high cranking currents but there are likely to be a lot more and deeper cycles than in an ICE car.
There has been a lot of discussion about using nominal 12 volt Lithium batteries in EVs but no major shift yet for a variety of reasons.

Some good information there. I am curious though as to what the parasitic loads are that an EV has that an ICE doesn't as you say they are higher. In an ICE if you sit with all the services on but engine not running that will drain the battery fast too.

 

[Deep purple]

In an ICE car the engine is usually rotating and in many cars this is what drives the steering pump, the AC and it also provides heating. In an EV the main motor only rotates when the car is moving so all the auxiliary systems are powered by electricity rather than directly driven by the main motor.
For a lot of the systems this electricity is 12 volts from the 12 volt battery. Some of the electrical auxiliary systems will not work unless the car is in RUN mode, but some will.
If you sit in the car with the systems ON but not in RUN mode you can turn various things on and off and watch the 12v battery voltage drop and then recover a bit when the load is turned off. This is because 12v battery voltage is driven by the state of charge of the battery, the temperature it is at and the charge/discharge current.
Over a short timescale (a few minutes) the state of charge and the temperature are fairly static so battery voltage is almost totally determined by the current going in or out. A big discharge rate will depress the voltage significantly, once the discharge rate is reduced to a small amount then the voltage will recover towards its floating state voltage.
Go out and play with the car in various modes and watch what happens to the 12v battery voltage on the panel and also the discharge current on the HV battery. Battery and cabin heating get into double figures of main HV system amps, which at nearly 400v is 4-5 KW!

 

[Mohammed]

I had same issue with mine few days ago where it would not even lock the door and l had take out battery left on charge over night for about 15 hours. Since then it been ok. So I would advise you to do same before you think to purchase new battery.

 

[Pebble]

Being new to the world of EVs and the MG5 Trophy, does the home wall charger (EVSE), apart from "charging" the HV side, charge the 12v battery as well? Or is it a case of the HV battery giving up some of its charge to the 12v one?
Sorry for the dumb question lol.

 

[Lovemyev]

Being new to the world of EVs and the MG5 Trophy, does the home wall charger (EVSE), apart from "charging" the HV side, charge the 12v battery as well? Or is it a case of the HV battery giving up some of its charge to the 12v one?
Sorry for the dumb question lol.

Hi and welcome to the forum !.
You are correct on both counts really.
When the car is on charge from your wall box, it will charge the 12 volt battery and when the car is in READY mode, the 12 volt battery is also being charged.
It should be noted that the 12 volt is NOT being charged when the car is in STANDBY mode however !.
It is therefore not recommended to have the car in standby mode for long periods of times, with electrical items running in the car.
Just leave the car in ready mode is a safer option.

 

[BugEyed]

To clarify, if your car is plugged into your charge point and actively charging the HV battery then the 12v will also be being charged. But if the car is not actively being charged, e.g. the car has terminated the HV charging or the charge point is not offering a charge (say it is on a timed charge) then the 12v is not being charged.
Nissan made a similar mistake with the 2011-2012 LEAF where leaving the car plugged in to a charge point actually discharged the 12v leading to cars with fully charged HV batteries and flat 12v after a couple of days. Mind you they rectified this in 2013 so you would hope that SAIC wouldn't make the same mistake.....
I've seen no evidence of the MG5 doing the industry standard top up of the 12v from the HV battery either on a schedule or when the 12v goes below a certain level. Whilst a "vampire" drain on the HV it only goes down a fraction of a % and I'd rather lose 1 or 2 miles range than have a flat 12v. I've not left the 5 unused for any period of time but the rejected MG4 survived a week at the airport without problem which implies that has something topping up the 12v even if the car is not run.

 

[Robf]

Soooo. If I pump up my tires with my portable compressor that plugs into the cigarette socket, it use the power from the 12v battery ?
Incidently I bought these to get around the issue of access to the tire valve without having to remove the plastic wheel covers, works fine.

Amazon product ASIN B0B6J6L8LY

 

[Lovemyev]

Soooo. If I pump up my tires with my portable compressor that plugs into the cigarette socket, it use the power from the 12v battery ?
Incidently I bought these to get around the issue of access to the tire valve without having to remove the plastic wheel covers, works fine.

Amazon product ASIN B0B6J6L8LY

Yes - You powering it from the 12 volt battery.
Will that adaptor fit your pump okay ?.

 

[Robf]

Yes - You powering it from the 12 volt battery.
Will that adaptor fit your pump okay ?.

Thanks, thought so, was trying to think of a way to avoid but couldnt (Maybe get the wife to sit in the car, turn it on and take the cable thro the sunroof.... or something like that ).
Yes the current tube and female fastener fits the male screw threaded end (sorry for being obvious) and is easy to push and seal on the valve with the covers in place.

 

[Pebble]

We found that when using a 12v inflator on previous ICE cars, the 12v ciggie lighter socket got very hot. To get around this, we chopped off the ciggie lighter connector on the inflator, put two crocodile clips on instead and hooked it straight up to 12v battery.