Can we go out and come in again. I know perfectly well (as do most people on the forum) that the LR battery will balance, at least to some extent, if charging is stopped at 80%. I am presuming that LR owners are setting this up on the app, however the app will not let you do that with the SR.
[Answering this slowly as I have a tennis match to watch. There may be some cross-posting.]
I think this thread is suffering from multiple interjections from people proffering information relevant only to LR batteries and which are possibly counter-productive when applied to the SR battery. Please, please, can we stop doing this, at least without specifying clearly that we're talking about the LR.
I don't know how you can stop an SR battery charging at 80% without cutting the power to the car. Maybe a wall box will do it? I genuinely don't know. I am trying to establish whether it is actually possible to create a situation where the SR would be
able to balance at less than 100% if it wanted to.
The theory I am, in my inexpert way, trying to explore, is that the OP may have a battery which has not been allowed to balance by being taken to 100%. We're told that balancing is more important for the LFP batteries. I've never seen mine
not balance when taken to 100%, even, once, when it was taken to 100% on five consecutive days. It really seems to want to do this thing.
If it's not possible to let the battery balance if the charge is stopped before 100%, then there are two situations where this might lead to trouble. One is the obvious one - the previous owner only used rapid chargers most of the time, without taking the trouble to finish off on a type 2 or a granny charger. Not good. The other is that the previous owner had been listening to all the injunctions to avoid taking the battery to 100%, "80% is health mode" and so on, and (unlike the LR battery) it hasn't been able to balance at this SoC - either because it intrinsically can't, or because it's not possible to stop it without cutting the power, which won't allow it to balance.
This, the first reply to the OPs concern about this state of his battery, worries me.
That does seem to have lost a bit, probably it has been charged to 100% daily or left at a high SOC.
No. That is advice which might be important and relevant if the battery in question was an LR, but it isn't. Cue yet another to-and-fro round of people advocating that SR batteries should also be operated most of the time below 80%, even though MG do not advise this, and have indeed specifically disabled the ability to do this via the app. More relevant, probably, is the article linked and quoted above.
I don't think there is any way that an LFP battery should be degrading as the OPs seems to have degraded after only a year and 8,000 miles, due to
having been managed exactly as MG tell owners to manage it, and exactly as that article says is perfectly fine.
I think leaping in to tell people with SR batteries that they should be going against MG's (and other expert) advice and preventing their battery from going to 100%, is not a good idea. You can see where it led to, posters questioning why the infotainment screen still has 80% marked as "health mode" (because MG's software has a lot of glitches in it, right?) and more exhortations to follow LR protocols with the SR, and SR owners feeling guilty because they don't do that.
If all that happens when a battery isn't allowed to balance is that the GOM becomes wildly unreliable, and there are no other ill effects, then maybe this is all of peripheral relevance. But if it's bad for the battery in other ways, then maybe the opposite of Jomarkh's suggestion is the case. Maybe this SR battery has been prevented from balancing for some reason, and what it needs now is a few opportunities to balance to its heart's content at 100%, and see what happens.
