Best of luck.
Just figure I'd give my 2 bits from what I've seen from doing this kind of thing several times myself... and discussions with others.
Although I guess it is a bit late now ... but for future reference of others ... I've done the subpack testing without removing the subpacks ... or disconnecting the orange terminal plates on the two sides ... it has risks , because the connected voltage is higher than with the side connection boards off ... but a set of alligator clips can connect to the + of one side and the - of the other side and do one subpack at a time that way ... has it's risks ... but is a bit faster ... and doesn't have the risk of the PTC strip damage from bending the thin metal.
When you do the testing ... I would suggest the following 4 steps / order:
#1> Do a Initial SoC discharge test of each subpack stick... how many Ah or Wh was each stick charged to initially?
#2> Do a discharge capacity check of each subpack stick from a fully charged state... once fully charged ... how many Ah or Wh will each stick give during a discharge?
#3> Note the subpack internal resistance estimate for each stick ... what is the change in terminal voltage from the resting state to the discharging state at a known amount of amps ... V=IR ... this can be noted during the above discharge capacity test.
#4> Note the estimated self discharge rate of each subpack stick ... fully charge the subpack stick after #2 above ... after a consistent number of days do a 2nd discharge SoC check ... note the difference in SoC Wh or Ah after the number of days compared to the capacity of Wh or Ah from a fully charged state.
Consistency is important ... it is more important that the cells / subpacks be close to matched to each other than being stronger ... similar SoC Ah/Wh is more important than higher Ah/Wh ... similar capacity Ah/Wh is more important than higher capacity Ah/Wh ... similar internal resistance is more important than lower less internal resistance ... similar self discharge rates is more important than lower self discharge rates... in order to compare the results yo get from each battery tested ... it is important the testing method is as consistent as is reasonably possible.
If you start at one subpack ... and proceed systematically ... by the time you finish doing the #2 & #3 testing and fully recharging of the 20th subpack stick ... many hours will have passed ... and you may be ready to start doing the #4 test of the 1st subpack stick.
The main benefit of this kind of subpack level testing is to quantify the condition of the battery pack.
A slow grid charger is a good method of doing occasional maintenance of a out of balanced SoC ... just keep in mind it treats the effect ... it does not fix the root cause of things like different internal resistance ... or different capacity ... or different rates of self discharge.