12v battery and Noco booster

[tsedge]

Perhaps a better design would be 2 smaller 12V batteries with the redundancy and failure detection showing when one is low (feed off one then the other so they are not the same state of charge - it could alternate to even out wear)?

 

[mg4mc]

Who'd have thought the logic to keeping a battery charged was so hard to get right!

 

[SMGYorks]

What SOC are you leaving the car at? There are rumours it doesn't charge the 12V battery if left below 50%.

39% the second time. I have 60% in my head for when it first happened, but can't remember exactly.

Checked that the battery terminal clamps are fitted properly and are tight?

Neither the Green Flag nor AA guys (don't ask!) who jumped it didn't spot anything physically wrong

I called MG, they said they'd take a look at its yearly service in a couple of weeks. But they seemed to think the problem was that I wasn't running it enough. I guess I've only done about 50 miles around town at the start of the week, and then not used it for a couple of days. They implied that there was no issue and I just need to use the car more.

Am I being unreasonable in thinking that I should be able to go a few days without using my car, and for the 12V battery not to die and immobilise the car?

 

[tsedge]

39% the second time. I have 60% in my head for when it first happened, but can't remember exactly.

Ok, try keeping it above 50 amd see if it happens again.

Neither the Green Flag nor AA guys (don't ask!) who jumped it didn't spot anything physically wrong

It could be a weak battery or parasitic drain. If nothing has changed lately then more likely the former - it might also be that the car is not quite charging the 12V enough and it periodically needs a spell on a battery charger. This could be due to a software bug.

I called MG, they said they'd take a look at its yearly service in a couple of weeks. But they seemed to think the problem was that I wasn't running it enough. I guess I've only done about 50 miles around town at the start of the week, and then not used it for a couple of days. They implied that there was no issue and I just need to use the car more.

Am I being unreasonable in thinking that I should be able to go a few days without using my car, and for the 12V battery not to die and immobilise the car?

This is BS, the car should keep the 12V battery topped up and you should be able to leave it for weeks while you go on holiday and still have it work when you return.

I wish dealers wouldn't make stuff like this up when they don't know what is wrong.

 

[Ian Key]

39% the second time. I have 60% in my head for when it first happened, but can't remember exactly.


Neither the Green Flag nor AA guys (don't ask!) who jumped it didn't spot anything physically wrong

I called MG, they said they'd take a look at its yearly service in a couple of weeks. But they seemed to think the problem was that I wasn't running it enough. I guess I've only done about 50 miles around town at the start of the week, and then not used it for a couple of days. They implied that there was no issue and I just need to use the car more.

Am I being unreasonable in thinking that I should be able to go a few days without using my car, and for the 12V battery not to die and immobilise the car?

I often only do a few miles a week, mainly less than a mile to take the dogs a walk on the park*, but I've not had a problem with the 12v battery. It sounds like a software issue which is preventing the charging the 12v battery when the car is locked.

*No I'm not being lazy taking the dogs in the car. One of them has problems with her feet and can't walk on hard surfaces.

 

[johnb80]

Perhaps a better design would be 2 smaller 12V batteries with the redundancy and failure detection showing when one is low (feed off one then the other so they are not the same state of charge - it could alternate to even out wear)?

Double the number of batteries, double the number of failure points.

 

[mg4mc]

Double the number of batteries, double the number of failure points.

True, if they can't keep one charged then what hope for two.

But lots of planes and boats have dual systems. I know in leisure boats it is usually a separate service battery for ancillaries, but you can switch them over to start the engines if the engine battery goes flat.

Hmm... Could you use the emergency power supply in the MG4 to kick enough life into it to turn on the HV. (Flight of fancy)

 

[tsedge]

Double the number of batteries, double the number of failure points.

I meant in a redundant configuration like with aircraft, so therefore more reliable, fewer failures and partial failure allowing a battery to be replaced/recharged while still operating the vehicle with no issues.

 

[JonnyG]

Had the MG4 for a year, never had an issue. If the HV isn't charging the LV it should be noticeable on the dash display. Really think this is blown out of proportion.

New owner here .. please can you explain where to look on the dash display and what we should see if charging and what if not charging ?. Sorry if this is obvious but I'm a newbie to the MG4. TIA

 

[Kithmo]

New owner here .. please can you explain where to look on the dash display and what we should see if charging and what if not charging ?. Sorry if this is obvious but I'm a newbie to the MG4. TIA

Scroll the right hand screen with the right joystick to the tyre pressure display and it will show the 12v SOC. With the car in ready mode it should show anything between 13.8 and 14.2v.
If you want to see the 12v battery's SOC with the car off then use the app, it's usually anything between 12.4 and 12.6v on mine.

 

[Rolfe]

I left my car in an airport car park (at 69% charge) for over two weeks and he woke up again as soon as I pressed the door button and I drove off. Lots of people have reported similar, and indeed longer periods of disuse.

 

[WonkoTheSaneUK]

I left my car in an airport car park (at 69% charge) for over two weeks and he woke up again as soon as I pressed the door button and I drove off. Lots of people have reported similar, and indeed longer periods of disuse.

Good to know, as I'll be doing exactly the same thing on Friday.

 

[KevW]

I've had a thought about all these 12v battery discharge issues and wondered if people who are experiencing these problems have lease vehicles? It's more and more common now that lease suppliers install trackers by utilizing the OBD2 port (as we found out on my wife's non MG company car). This has a permanent live supply and will surely cause a drain on the battery, whether it's enough to flatten it I'm not qualified to say but I'm guessing that if the vehicle is used mostly for short duration trips the HV may not have enough time to fully recharge the LV battery so you get a downward spiral to discharge. A rule of thumb though would be that a 12v battery at rest should read around 12.7-13.0v and if yours is consistently below this I would change it.

 

[Martinonline]

I bought my car outright in April and not had a battery problem until yesterday (reported in another thread). Currently I am seeing resting voltages below 12.7v. I only do short journeys with a long one once a month so that may be the cause of the low voltages. I am monitoring it.

 

[Coulomb]

It's more and more common now that lease suppliers install trackers by utilizing the OBD2 port (as we found out on my wife's non MG company car). This has a permanent live supply and will surely cause a drain on the battery, ...

That's an interesting idea. Well worth looking into. Any suffering owners want to chime in?

A rule of thumb though would be that a 12v battery at rest should read around 12.7-13.0v and if yours is consistently below this I would change it.

12.7-13.0 would be a brimming full battery, at rest with a very light load. I would put the "change if below this" figure much lower, around 12.2 V at most, considering how the car has a low drain all the time. Well, it should be low, I'm guessing of the order of 20-50 mA.

Edit: And don't forget that merely walking near the car with the keys in your pocket or handbag will be enough to increase the drain, and opening the door will "open the flood gates" so to speak, compared to the truly sleeping long term drain.

 

[MGFour]

I've had a thought about all these 12v battery discharge issues and wondered if people who are experiencing these problems have lease vehicles? It's more and more common now that lease suppliers install trackers by utilizing the OBD2 port (as we found out on my wife's non MG company car). This has a permanent live supply and will surely cause a drain on the battery, whether it's enough to flatten it I'm not qualified to say but I'm guessing that if the vehicle is used mostly for short duration trips the HV may not have enough time to fully recharge the LV battery so you get a downward spiral to discharge. A rule of thumb though would be that a 12v battery at rest should read around 12.7-13.0v and if yours is consistently below this I would change it.

Are you sure it the lease company and not your wifes workplace that instigated it, sounds like it could be a stealth way of them tracking their workforce rather than lease company, never heard of a lease to do that. But yeah if something is installed taking a permanent drain it defo wont help.

 

[tsedge]

My battery reads between 12.1V and 12.8V when not being charged and I have had no problems so far (after 6 months). Usually it is 12.3V or above but I have seen lower.

 

[KevW]

That's an interesting idea. Well worth looking into. Any suffering owners want to chime in?

12.7-13.0 would be a brimming full battery, at rest with a very light load. I would put the "change if below this" figure much lower, around 12.2 V at most, considering how the car has a low drain all the time. Well, it should be low, I'm guessing of the order of 20-50 mA.

But that's the point, with the HV pack connecting every time the vehicle is in ready mode there is no reason for the LV battery to be anything less than 'brimming'. The HV should be charging the LV at around 13.8v every time you use it.

 

[KevW]

Are you sure it the lease company and not your wifes workplace that instigated it, sounds like it could be a stealth way of them tracking their workforce rather than lease company, never heard of a lease to do that. But yeah if something is installed taking a permanent drain it defo wont help.

No it's the lease co's policy, not unusual especially for big fleet contracts...

 

[tsedge]

No it's the lease co's policy, not unusual especially for big fleet contracts...

It may also be insecure, depending on the device and configuration.