Replacement 12V auxiliary battery for MGS5

[stevedee]

...I think I'm probably better off starting another thread, this is a complex subject...

Yes please, I'll join you.

 

[MG Clive]

Yes please, I'll join you.

See here - Recovering a Lead Acid battery after it has been deeply discharged

 

[T1 Terry]

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

The 35Ah battery as supplied is puny 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?

Can you give me the dimension of the battery please, from there I expect I can guide you to a suitable alternative that is fast charging so will charge in the short blips of charge current/voltage it receives ....

T1 Terry

 

[Joningy]

A lead acid battery needs to remain at charging voltage, above 13.6 V min, to actually recharge. 13.6 V will maintain the charge at 100% if it is already at 100%, it will bring a battery up to about 50% SOC if it stays at that voltage for 24 hrs or more, but that is no enough voltage to over come the inherent internal resistance of any type of lead acid battery.

Now, if the battery was not saturation charged when built, it will already begin sulphating ..... within 12 hrs actually .....

If the terminal voltage is held at 14v for 12 hrs or more, you can get closer to fully charged, as long as the plates are not sulphated. Once the sulphation starts on lead acid plates, no chemical reaction can occur in that part of the active plate, so capacity is lost.

I think I'm probably better off starting another thread, this is a complex subject, I'll skim over it as much as possible, but I'm happy to dive deeper if anyone wants to know more

T1 Terry

Very interesting Terry, I'd be interested to know more!

 

[Joningy]

A quick update on my S5 parked at Gatwick Airport, I tried to remotely access the MG iSmart app this morning but, I was unable to get any response from it, timing out each try.
Does this mean my 12v battery has already drained in 7 days, or does the app "go to sleep" after a period of non use?

My MG4 stayed awake for 2 weeks, but after this time, it refused to connect to the iSmart app, but still stared up without a problem after nearly 4 weeks, I'm hoping (rather unbelievably) the S5 will still be OK when we try to start her up in another 2 + weeks time, can't see it TBH after my previous experience of the 12v going flat in less time.

 

[stevedee]

The car goes to 'sleep' and iSmart has no way of waking it. I think it will be fine when you get back to it.
Our S5 won't be touched again until the end of the month ...let's see how that ends!

 

[MG Clive]

The car goes to 'sleep' and iSmart has no way of waking it. I think it will be fine when you get back to it.
Our S5 won't be touched again until the end of the month ...let's see how that ends!

Should be interesting.

 

[TimothyN]

I was away in the Caribbean for 2 weeks last month and the car was fine when I got back.

 

[stevedee]

Our S5 won't be touched again until the end of the month ...let's see how that ends!

Our car was charged to 80% on Monday.

I understand EV batteries don't suffer power 'leakage'. However, during this period, it will be maintaining the 12V battery, which in turn is powering vital services within the car.

Working with AI, I used likely daily temperatures for the next 2 weeks, specified the car was facing the morning sun at a coastal location, and this is what I've come up with:-

- Possible daily draw on EV battery (to maintain 12V battery) ~0.2–0.35 % SoC per day

- 28 day estimate: 0.25–0.30 % × 26 days ≈ 6.5–8 %

In terms of energy (usable ≈ 61.5 kWh):-
- 6.5 % ≈ 4.0 kWh
- 8 % ≈ 4.9 kWh
- 9 % ≈ 5.5 kWh

Best (conservative) guess after 28 days: ~72–74 % SoC

We shall see!

 

[T1 Terry]

Our car was charged to 80% on Monday.

I understand EV batteries don't suffer power 'leakage'. However, during this period, it will be maintaining the 12V battery, which in turn is powering vital services within the car.

Working with AI, I used likely daily temperatures for the next 2 weeks, specified the car was facing the morning sun at a coastal location, and this is what I've come up with:-

- Possible daily draw on EV battery (to maintain 12V battery) ~0.2–0.35 % SoC per day

- 28 day estimate: 0.25–0.30 % × 26 days ≈ 6.5–8 %

In terms of energy (usable ≈ 61.5 kWh):-
- 6.5 % ≈ 4.0 kWh
- 8 % ≈ 4.9 kWh
- 9 % ≈ 5.5 kWh

Best (conservative) guess after 28 days: ~72–74 % SoC

We shall see!

I think they are referring to the 12v aux battery failing or seriously discharging to the point the car won't turn on or even let you in without the manual key method.

It will be interesting to see if it is a problem with the app continually waking the car up, but being so far away, it is no longer a bluetooth thing but a network connection required .....

T1 Terry

 

[stevedee]

I think they are referring to the 12v aux battery failing or seriously discharging to the point the car won't turn on or even let you in without the manual key method.

It will be interesting to see if it is a problem with the app continually waking the car up, but being so far away, it is no longer a bluetooth thing but a network connection required .....

T1 Terry

Yes, I'm sorry if I'm drifting too far.

This test is part of showing that the 12V battery should not fail when the car is left unused, that it is defo maintained by the EV high voltage battery and it is unnecessary to look for a 'better' 12V battery to replace the original.

I'm pretty sure there is no mechanism for the app (iSmart) to 'wake up' the car once it falls into a deep sleep state.
Also, the app cannot Bluetooth with the car, it has to communicate via server/cloud software which deals with car comms.
All the app does is poll the server software for data, and shows last data available (historic) if it can't get up-to-date data.

 

[Joningy]

Let's hope you are correct @stevedee when you say the HV traction battery "hopefully" maintains the 12v battery whist "asleep". At least I think you mean that!

As we've already discussed, MG maintains it's doesn't do that!

We'll soon see now as we are due back to Gatwick in under 2 weeks.

I'll be reporting back here (hopefully) either way, but I'll be extremely pleased not to have to manually unlock the car and reach out for the jump starter pack in the dark and cold of the airport parking lot

 

[Joningy]

I'm normally a positive person, but in this case, I'm not even "sat on the fence"
I'm negative and untrusting of the durability of my MGS5 12v battery
A strong and uncomfortable feeling of Déjà vu, saying very little to my wife to save her form worrying.
Just hope I can find my keys at the airport, unlike last year's episode of losing my MG4 keys whilst abroad in Corfu.

 

[T1 Terry]

I'm normally a positive person, but in this case, I'm not even "sat on the fence"
I'm negative and untrusting of the durability of my MGS5 12v battery
A strong and uncomfortable feeling of Déjà vu, saying very little to my wife to save her form worrying.
Just hope I can find my keys at the airport, unlike last year's episode of losing my MG4 keys whilst abroad in Corfu.

You are being positive, you are sure it won't start

T1 Terry

 

[Joningy]

You are being positive, you are sure it won't start

T1 Terry

Technically you are spot on Terry, I'm absolutely sure the effing car aint gonna start without the jumps start pack, history dictates!

 

[stevedee]

Let's hope you are correct @stevedee when you say the HV traction battery "hopefully" maintains the 12v battery whist "asleep".

Of course, if our S5 12V battery IS dead when we get back at the end of the month, you'll never hear from me again!

(We've got as far as Madrid airport, only another 5,500 miles to go!)