Gen2 cells in Gen1 battery - lid won’t fit? Also - in-car block balancing question

I rebuilt my battery on my 2002 NWH11 bought in Dec 2019 (and ended up ‘sitting’ for over a year due to Covid19 - all the original cells self-discharged very badly);

I rebuilt it using NWH-20 cells (I bought two full NWH-20 batteries a few years back; interestingly they didn’t self-discharge like the NWH11 ones).

After carrying it to the car and refitting it (without lid; it is kind of heavy for one person), I discovered an issue : the ‘top case’ that is supposed to cover the battery ‘won’t go on’ - at least not properly. It is hovering perhaps 8mm, to the extent the battery can’t be screwed into the car (I managed with one bolt; enough for now).

I didn’t force the lid too much (a short circuit would not be much fun), I didn’t leave any tools in there.

Is there an issue with the ‘wider’ NWH20 cells stopping the battery lid going on? I ask as the gaps surely won’t be great for the cooling; I only need to get the annual safety check (WOF in NZ) done this weekend, but do need to get the lid on properly for actually driving!

A partially related question; I charged the blocks to 16.8 volts over two weekends, using lower and lower voltages, keeping notes etc. They went out of balance discharging (parked up, headlights on, battery went to ‘full’ then eventually showed ‘nearly full’). I grabbed one of my NIMH chargers (up to 14 cells so can do a block each time) - picture related - and topped up the lower cells....... then ran the car till battery went low, the engine started and charged it, etc - to be topped off any low cells - and after that, the battery stayed in balance (for now...); I will keep one charger and a charger 12v battery as a power supply to ‘fix’ any cell imbalance if I breakdown, and I plan to road-test this Prius as a daily driver soon.

So, in addition to ‘does the battery top cover usually ‘not fit’ due to wider NWH20 cells’, my other question is:

How stupid is it to charge a block / 2 modules at a time, using a NIMH charger, with the car switched off, but with the HV battery fully configured with all bus bars etc? Basically connecting the charger across two modules, and the charger is not earthed to the car in any way, and you only touch the charger with an insulated object to control it? (I assume the answer is ‘madness’, and I know a short could melt the charger, and 300 volts is enough to kill perhaps 8 people at once by cardiac arrest or seizure). But it worked in my case... (not recommended at all; in my role as a hospital doctor, one false move is guaranteed and instant electrocution).

 

Regarding the picture - I did clean the bus bars in the voltage sense side before refitting, and I did do the battery rebuild in my NWH20 Prius

 

Unfortunately I did put all the screws in - after this photo, so they are centered to the base of the battery; however I will check, because despite being screwed in, they might be a millimetre or two ‘off’ to one side, which might explain it!