Replacing Transaxle

Hey everyone, thanks for all the input so far, apologies for the quiet few days since last post.
So I had my laptop connected to it to get the inf code 388 for P3000. This presented itself af the time of failure when the car was running, in fact it was doing 80mph up a steep dual carriage way incline, so it's power demand was being maxed out. So I'm not dismissing the fact it 'could' be the battery as per error code with that specific INF code.
However, I'm suggesting that INF code came from a fault on the BMS (because I opened it up) where a litlle burn hole appeared on one of the chips.
While the mechanical failure whilst driving appeared under full load as above and sheared the transaxle damper plate nuts right off. That or the input shaft has snapped. I'd like to hope the plate fell off due to shearing of all the bolts because they may have worked themselves loose enough to get weakend. I'm also suggesting this because I heard that intermittent metallic rubbing in the days/week before it actually failed catastrophically.
The other question is, did that hole in the chip in the BMS appear after the fail, or was it the cause of it? (photo below)
I did suspect that could have been the cause and replaced the BMS with another one and at the same time charged the batteries a little bit (off the car). So it has been out for renewal, and it's now back in, and showing the same symtoms.
TBH, I was pretty chuffed about being able to take the battery apart enough to give it a good clean of the copper plates (lemon juice did it) new M5 bolts, re-torque, balance the cell pairs enough for the car to not reject it. However, I might need to do it all over again, which would be a right pain, but I might fork out for a new one because I didn't go all out with testing individual cells (their internal resistances checked out quite similar at under 20mOhms, I'll only fork out for a new (renewed from a specialist not new from toyota) one if I can eliminate a mechanical fault, which I suspect it may very well be. So no new codes appeared.
This is why I'm hoping it's mechanical.
The problem is it's parked on the street (half on a pavement, half on the road), so I can't do much myself underneath unless I can move it onto the drive, but the brakes are probably seized due to rust, it hasn't moved for months. The 12V battery got charged while the other was out. So no faults reappeared when the battery went back in the other week, but the bars drop fast when it tries to start. So I've got maybe another two tries left.
At this point should I ask a transmission specialist to pop the gearbox off and take a look at the input shafts or the condition of the transaxle plates before I scrap it?