Replacement 12v auxiliary battery for MGS5

[Joningy]

I've searched long and hard to try to find a decent quality replacement 12volt auxiliary battery for my troubled MGS5 with zero success.

The 35Ah battery as supplied is pewney at best and may benefit from doubling the capacity to 60 or 70Ah, there doesn't appear to be a like for like (35Ah) swap in a reliable brand made yet.

But there's plenty of of slightly taller and longer, with similar width available which may be persuaded to fit.

Ideally I'd prefer to up the capacity, but I don't really want to mess with the warranty conditions by making new and possibly irreversible battery mounting kit.

Have any of our fellow DIY, happy to "have a go" guru's thought along similar lines?

 

[Ian Key]

I fitted a Yuasa YBX5012 12V 54Ah to my MG4 without having to alter the mountings.

 

[Joningy]

I fitted a Yuasa YBX5012 12V 54Ah to my MG4 without having to alter the mountings.

What was the original capacity of the MG4 battery Ian?
Although I had an MG4, I never needed to look at the battery.

 

[MG Clive]

What was the original capacity of the MG4 battery Ian?
Although I had an MG4, I never needed to look at the battery.

Mine is 45Ah.

 

[Joningy]

Mine is 45Ah.

Interesting, so MG have reduced the MGS5 12v battery capacity by almost 50% on a car that possibly needs more capacity than the MG4, seems a case of penny pinching too far, although my local Penton MG have had several MG4's loosing 12v power, but mine was the first S5 battery to play up with them.
I've had a quick look at the battery mounting, I think it'll be possible, but there's an "Engine Bay Brace Reinforcement bar" just about giving enough clearance to get a bigger capacity battery under, it may mean the removal of the brace to drop the new larger dims. battery into.

Is this why they've left out certain items, such as 12v auxiliary battery monitoring on the app??

Interesting, so MG have reduced the MGS5 12v battery capacity by almost 50% on a car that possibly needs more capacity than the MG4, seems a case of penny pinching too far, although my local Penton MG have had several MG4's loosing 12v power, but mine was the first S5 battery to play up with them.
I've had a quick look at the battery mounting, I think it'll be possible, but there's an "Engine Bay Brace Reinforcement bar" just about giving enough clearance to get a bigger capacity battery under, it may mean the removal of the brace to drop the new larger dims. battery into.

Is this why they've left out certain items, such as 12v auxiliary battery monitoring on the app??

OH really @MG Clive , I was fed some duff info then perhaps Clive, or my memory is fluked up.
Up to date info on anything S5 is very sketchy at best at the moment.
I'll do a bit more research on the net and under the bonnet before ordering anything.

 

[stevedee]

...The 35Ah battery as supplied is pewney at best and may benefit from doubling the capacity to 60 or 70Ah, there doesn't appear to be a like for like (35Ah) swap in a reliable brand made yet...

If your car is functioning properly, the 35Ahr 12V System battery should be frequently charged from the main traction battery.

On our Long Range S5, the main battery has a capacity almost 2000 times greater than the system battery.

If the car has a fault, and is not maintaining the System battery (...and an alarming number of users on this forum are reporting 12V battery issues) then replacing the 35Ahr with a 70Ahr may mean you can survive for twice as long before that too, goes flat.

But it won't solve the real issue.

 

[Joningy]

If your car is functioning properly, the 35Ahr 12V System battery should be frequently charged from the main traction battery.

On our Long Range S5, the main battery has a capacity almost 2000 times greater than the system battery.

If the car has a fault, and is not maintaining the System battery (...and an alarming number of users on this forum are reporting 12V battery issues) then replacing the 35Ahr with a 70Ahr may mean you can survive for twice as long before that too, goes flat.

But it won't solve the real issue.

Yes totally understand that logical condition @stevedee, I haven't yet got to the bottom of the cause of my 12v battery loosing power, MG think it's solely down to my permanent live dash cam, which I've now changed to switched, but the car hasn't been standing idle long enough since it was in for inspection over a week ago.

Time will soon tell Steve, we will be leaving the car at Gatwick for over 3 weeks as from Monday next, that'll give me the acid test I'm looking for (or not )

Quite expecting to return to a flat 12v battery if the traction battery doesn't kick in to maintain it.
MG customer service have stated, somewhat ambiguously, this does NOT happen... Soon see!

I've had a thought though, and more knowledgeable MGS5 folk may be able to help here perhaps.

If I can remotely activate the car via the app for say half an hour to an hour once per week, the HV battery should top up the 12v and maintain the level of charge???

Thoughts on this approach please!

 

[MG Clive]

OH really @MG Clive , I was fed some duff info then perhaps Clive, or my memory is fluked up.
Up to date info on anything S5 is very sketchy at best at the moment.
I'll do a bit more research on the net and under the bonnet before ordering anything.

What 'duff info' do you mean @Joningy ?

 

[stevedee]

...MG think it's solely down to my permanent live dash cam...

Smells like cow ...no wait, its Bull!

Time will soon tell Steve, we will be leaving the car at Gatwick for over 3 weeks as from Monday next, that'll give me the acid test I'm looking for (or not )

3 week holiday sounds great, can you say where to?

Our car will soon be standing for 24 days when we whizz off to central America ...that will also be another test!

...Quite expecting to return to a flat 12v battery if the traction battery doesn't kick in to maintain it.
MG customer service have stated, somewhat ambiguously, this does NOT happen... Soon see!

Yes, what are they saying?

...If I can remotely activate the car via the app for say half an hour to an hour once per week, the HV battery should top up the 12v and maintain the level of charge???

No, not helpful.
Just enjoy your holiday and forget about 'baby'

Worst things can happen than a flat ev battery;

#1 son came back to airport v.late at night to find the parking brake on his Tesla would not release.
Ever considered how you remove a heavyweight car from a multistory car park, when the brakes wont release?
Tesla had to send out a special thing that goes under the car, lifts it up a few inches, then an operator with remote controls manoeuvres the car out.

That was followed by the long fight with airport parking, who thought he owed them hundreds for the time it took to be removed!

 

[Joningy]

I was somehow led to believe the S5 has a 35Ah 12v battery Clive, perhaps I was mistaken, but I've just scanned the owners MGS5 manual again and can't see the value for the battery,.
I can't remember where I got the idea it's 35Ah, hopefully I'm wrong and it's larger.
But whatever capacity, a lot of people are suffering similar problems.

 

[stevedee]

I was somehow led to believe the S5 has a 35Ah 12v battery...

Ours is 35Ahr; just lift the bonnet and take a look, the rating label should be visible.

 

[MG Clive]

I was somehow led to believe the S5 has a 35Ah 12v battery Clive, perhaps I was mistaken, but I've just scanned the owners MGS5 manual again and can't see the value for the battery,.
I can't remember where I got the idea it's 35Ah, hopefully I'm wrong and it's larger.
But whatever capacity, a lot of people are suffering similar problems.

OK, but what is making you think that 'being led to believe it has a 35Ah battery' it's duff info ?

 

[Joningy]

OK, but what is making you think that 'being led to believe it has a 35Ah battery' it's duff info ?

I'm not sure it is duff info now Clive, if the MG4 is 45Ah and the S5 IS 35Ah, just seems a step backwards, but I really cant find out exactly the size!

 

[MG Clive]

I'm not sure it is duff info now Clive, if the MG4 is 45Ah and the S5 IS 35Ah, just seems a step backwards, but I really cant find out exactly the size!

@stevedee has confirmed his is 35Ah.

 

[Joningy]

Smells like cow ...no wait, its Bull!

3 week holiday sounds great, can you say where to?

Our car will soon be standing for 24 days when we whizz off to central America ...that will also be another test!

Yes, what are they saying?

No, not helpful.
Just enjoy your holiday and forget about 'baby'

Worst things can happen than a flat ev battery;

#1 son came back to airport v.late at night to find the parking brake on his Tesla would not release.
Ever considered how you remove a heavyweight car from a multistory car park, when the brakes wont release?
Tesla had to send out a special thing that goes under the car, lifts it up a few inches, then an operator with remote controls manoeuvres the car out.

That was followed by the long fight with airport parking, who thought he owed them hundreds for the time it took to be removed!

Lanzarote Steve, It's an annual migration to warmer climes!

MG's comment already posted here, but I'll post again:-

"Thank you for contacting MG Customer Care.

I t is possible for the system to monitor the 12 volt auxiliary battery, however this typically occurs only when the vehicle is actively charging or when the vehicle is being driven. When the vehicle is left unattended and remains unused for an extended period, the 12 volt battery may naturally lose charge, as would be expected with any motor vehicle under similar conditions.

Best regards,"

Slightly ambiguous perhaps, I'll leave you to form your own ideas!
Even the supposedly "rock solid" Tesla has problems, hope it was successfully resolved?

 

[stevedee]

Lanzarote Steve, It's an annual migration to warmer climes!

Well at least you will be recharging your biological batteries, have a great time!

I t is possible for the system to monitor the 12 volt auxiliary battery, however this typically occurs only when the vehicle is actively charging or when the vehicle is being driven.

You may have already seen this data plot...

...which proves that the 12V battery is typically charged, even when ev is not being charged & traction battery SoC is as low as (at least) 15%.

Even the supposedly "rock solid" Tesla has problems, hope it was successfully resolved?

Yes. And he has had a new ev battery since then (but not related to his first problem).
Both he & his wife have Teslas.

 

[Joningy]

Yep, mine is defo 35Ah. No