That's my four cell swap completed and the car back on the road on Tuesday.
I took loads of pictures but posting them here is a real PITA as it's the only forum I use that doesn't support uploading attachments, and uploading them elsewhere and linking is a bit of a pain for lots of photos to be honest.
Apart from things like rusty bolts everything went fine except for one mistake I made - I matched the Voltage/SoC of the replacement cells at 20% SoC rather than 100%.
So as they charged up the newer higher capacity cells "fell behind" as they would need more charging to reach 100%. So at full charge they ended up 50mV lower than the other cells. (4.05 v instead of 4.1 volts)
Of course the cell balancing system valiantly spent 3 hours trying to balance the cells at the end of the normal charge cycle but finally had to give up after making little headway. 50mV less is approximately 5% of the entire capacity of the battery so assuming about 40Ah that is a 2Ah error in cell balancing between original and replacement cells.
With 100mA capable balance resistors it is going to take at least 20 hours of balancing time to correct this mistake!
I tried using the "Voltage equalisation" procedure in Diagbox (which I believe is the same as the Cell Smoothing feature in MUT-III) however it aborted after less than an hour so the only option seems to be to simply let the balancing system pick away at it bit by bit at the end of every charge cycle, and it seems to be willing to do about an extra two hours of balancing after reaching 100% before timing out and ending the charge session without achieving balance.
The car is working fine but due to this the usable capacity will be limited by the imbalance so I'm probably not going to attempt the battery calibration procedure until after adequate balance has been established, which make take around a month.
Meanwhile the BMU has made a small Ah adjustment itself. The day after I refitted the battery it went down from 33.0Ah to 32.9Ah - which will just be modelled degradation, but then this morning after three days commuting totalling about 100 miles driving it bumped the figure up to 33.9Ah which is higher than it was when I removed the battery.
This seems to align with what happened during jray3's battery swap where the BMU would gradually bump the Ah up by 1Ah every few hundred miles, so it will be interesting to see where it gets to by the time I'm ready to do the battery calibration.
For those of you who have had your battery packs out before I have a piece of advice - check the rubber grommet/seal for the battery air intake is properly engaged in the bodywork!
It might not be immediately apparent but when you jack the battery up into place again it's impossible to properly engage the air intake grommet simply by raising the battery - the grommet will be partially crushed against the body and not sealing.
You must lift the carpet and remove the air duct from the grommet to the AC system to get access to pull the grommet through and engage its slot into the bodywork hole properly then refit the air vent. I have pictures detailing this.
If this is not done road spray may be able to enter the battery pack through the air vent.