Ian and I took one of my 7 Seven subpack Prius based packs and after discharging it to lower the SOC by 10-20%, set up a constant 300MA charge system, and logged the voltages across each subpack. We spread the packs out so that cooling would be the same on each, and measured the temp of each cell when we took the voltage measurement. The initial condition showed a max of about .07V difference between the subpacks. The charge ran for 14 hours before I saw the sides of the cells start to bulge, but I never saw any measurable temperature rise.
The Subpacks seemed to equalize starting at 7.85V/subpack, where all of the subpacks were at that exact voltage. I continued to charge up to 8.47V/subpack where all the subpacks remained at the exact same voltage.
Next I will discharge the series string and log the voltages during discharge.