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Discussion Starter #1
We had our 10 month old ZS serviced at our local main dealer - Tomey Basildon - end of November. 1st Year service and Comfort 2 update (Paid for). No indication if the car took the BMS update. Maybe part of the first service?

Since the service the feeling has been the range is much lower than before.

Initially I was putting this down to the cold weather. Having read the posts on the FB page, I do believe there is more to it than just the weather. So started to collect some data in the last day or so.

Charged the car overnight using our Home 7kW Rolec charger before using the car for a 66 mile round trip yesterday. Noted when we went to disconnect the car, the MG symbol was still illuminated (Not pulsing) so if I understand correctly this means the battery was balancing (Correct term?). Started out drive with 133 on the GOM. Driving cycle was about three quarters Motorway, rest B roads up to 50 mph. We did drive about 70mph so, yes, heavy footed on the Motorway. Drive cycle gave 2.8 miles / kilowatt. Returned with 34 miles on the GOM. Two further short trips during the day, one 3 miles and one 13 miles. Wife commented on the 3 mile drive, GOM dropped 10 miles in one go. After the 13 mile round trip, returned with --- and putting the car on charge, 4% left on the battery.

So mileage for the day was 82 miles. Battery not fully balanced.

I did not do the last two drives. Budgeting 2.8 miles per kilowatt overall for the day, and assuming the battery was fully charged, I would have expected about 124 miles instead of 82.

Coming back to the overnight charge, monitored overnight last night. To charge and complete balance - MG light off, was 10 hours. Seems a long time?

I would welcome thoughts if members believe I have a issue here and if so what other data should I collect before contacting the Dealer?
 

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Discussion Starter #2
Update from today. Wife drove the car 20 miles this morning. 7 miles on a dual carriageway at 70 mph. Rest urban driving / B Roads. Trip stated 2.3 miles / kW! GOM dropped from 149 to 86.Battery gauge showing five bars.
 

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Drive cycle gave 2.8 miles / kilowatt.
Did a 32ish mile round trip today. 0c for whole trip on mainly A roads. I also returned 2.8 m/kWh. I don't think the MG likes the cold.
MG light off, was 10 hours. Seems a long time?
Can take an awful long time to balance if it's not been balanced recently and it's very cold. Zoe sometimes could take 3 to 4 hours to do the last 1%.
Trip stated 2.3 miles / kW!
That's worryingly low.

I've only had the comfort update so far, but there's been a lot about the BMS and heater updates being dodgy. They're both supposed to be abandoned, but I wonder if you're dealer doesn't know this and has actioned them in error?
 

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This is the battery heating update that’s destroyed the range, right?
 
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This is the battery heating update that’s destroyed the range, right?
No, its not the battery heater update.

It's the BMS. And the BMS update changed sometime between August and November. August BMS update is ok. November BMS update kills range. First it makes the GOM go crazy, then it sorts itself out by using a really low miles per kWh. I believe the m per kWhr is not just measured, but estimated based on change in battery percentage, estimated battery capacity and miles traveled. With the bad BMS update, the battery capacity is considerably reduced, which then causes the car to give really bad miles per kWh as it tries to match battery percentage against the capacity which is much lower than it expects.
 

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....
I would welcome thoughts if members believe I have a issue here and if so what other data should I collect before contacting the Dealer?
I think the dealer might prevaricate and ask questions about the car settings, such as:

Interior heating in use initially for demisting/ de-icing?
On journey - using heated seats only? or main cabin heating ?
And what driving modes for recording the GOM values?
 

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It's very easy to check - look at the voltage once fully charged/balanced. If it's around 430V, you've lost 20-30% of the battery, and have bad BMS. If it's around 450V, all is good.

This should be all the dealer needs to know. There is a curve of energy in battery, which increases with voltage of battery. Each car will have a slightly different curve, but they will be within a few volts of each other.
 

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There is a thread on this over on mgevs.com where I did some testing, I'm assuming when mine was updated in September it will have been the earlier BMS update from August, which is why mine is showing 455V at full charge (subsequent posts show other users identifying they can't put the full remaining amount back into the battery to get to the usabke 42.5 at 100%) - BMS update-Computer says “No”
 

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I had the Comfort 2 update and latest BMS done on August 5th last year, GOM range indicated about 214 miles fully charged. When I found out about the HV Battery Fuse update I was concerned so had that done together with the traction battery update. Latest BMS update applied. Range went back to the more normal GOM reading of 164 miles.

I decided due to increased virus restrictions to have its first annual service done a couple of weeks early on 23rd October. I understand that that the mechanic re-installed the current BMS update on that date as I had mentioned the car would still not charge with the car door open or unlocked. Problem resolved. I have had no updates since.

Currently I obtain 110 - 135 in temps of -2 to +2 Deg C. Full charge GOM indicates between 154 and 159 miles. Cumulative reading over 500 miles since service is 2.7 kW/mile. Daily readings are between 2.9 and 3.2 kW/mile (hilly rural, wet, cold, muddy, windy, icy!). Fully charged battery voltage is 456V consistently.

It appears therefore that sometime after 23rd October the BMS update changed to cause the reduced range for those who updated at some point after that date.

I am holding off on all future updates until the picture becomes clearer.
 
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Mine had first service with bunch of updates in November, had no chance to properly test it before Christmas due to work break, now back on my usual 65 miler a day and i'm in shock to how low capacity available I can see compared to winter year ago, 4 days in testing and by calculating %used versus what is pumped in to car over night it shows around 33kWh available battery capacity, doing 65 miles a day on A-roads with avg 3.1 mpkWh i'm bk home with 1 max 2 blobs and battery warning, in summer bfre updates I could do two days on one charge. Battery Volts 439...unfortunately I don't have value from before updates but looks like around 455 on 100% is sort of correct for full capacity
 

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Hi all,
I've had confirmation today that MG has spotted a bug in the BMS code from the recent August/October updates.
It looks like the August update caused cell balancing issues when full (so the end balance took 5hours or so). They tried to rectify this in the October update, but then found that this caused cell balancing issues when SOC was lower. This has caused range issues, as the car isn't able to use the full pack capacity.
By the end of next week, there will be a new BMS update released to the dealer network, which will be able to fix the affected vehicles.
 

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Hi all,
I've had confirmation today that MG has spotted a bug in the BMS code from the recent August/October updates.
It looks like the August update caused cell balancing issues when full (so the end balance took 5hours or so). They tried to rectify this in the October update, but then found that this caused cell balancing issues when SOC was lower. This has caused range issues, as the car isn't able to use the full pack capacity.
By the end of next week, there will be a new BMS update released to the dealer network, which will be able to fix the affected vehicles.
That's good news Miles. But are we going to be 'recalled' by the dealers to rectify this?
 

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Thanks @Miles Roberts for this info.

I will get mine updated ASAP.
 

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Discussion Starter #15
Thanks for all the replies folks. Really appreciate it.

After a balanced recharge I am getting 438v.

I had heard about the BMS SW issues and heard that MG were working on a fix. @Miles Roberts great to hear they have the fix due end of next week. I assume the original BMS update would have been done FOC as part of the service. It was not mentioned on the paperwork.

I will contact the Dealer now.
 

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Thanks for all the replies folks. Really appreciate it.

After a balanced recharge I am getting 438v.

I had heard about the BMS SW issues and heard that MG were working on a fix. @Miles Roberts great to hear they have the fix due end of next week. I assume the original BMS update would have been done FOC as part of the service. It was not mentioned on the paperwork.

I will contact the Dealer now.
Your dealer may not have heard about the update yet - I got the information from one of the Longbridge Engineering Team. The dealer aftersales bulletin will probably not get to dealers until next week.
 

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Discussion Starter #17
OK. Thanks. I have booked a placeholder for 21st. I will check a couple of days before to see if the update is available.
 

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My car is due it's first service on the 15th Jan and hopefully the wiring loom replacement recall in the divers door, but others like myself appear to be having problems obtaining the affected part ?.
Can @Miles Roberts confirm that THEY have any issues regarding availability please of this item.
My car was also booked in for the latest software updates, that did included the HV battery fuse update.
Would it be wise to go ahead with this single update and leave any other updates for another date in the future ?.
Many thanks for the info Miles.
 

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I have just booked mine in for Friday to get the new BMS update so hopefully, I will be back to 450v charges and get my range back I will report back and let you know what issues it brings
 

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Discussion Starter #20
Via Facebook, I exchanged messages today with someone who took the update yesterday at the same dealer I am booked into on Thursday.

Maybe most people on here have read extensively about the BMS, especially if you have had range issues. Looks like it may take a few few charges and balances to get the battery back to full capacity. I will leave my feedback on here.

@damo2929 I look forward to your feedbacks.
 
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