Just wondered why you stopped charging so soon as personally always try to get past 10% but I know it's a bit sad timing how long it takes to go from 8 - 9% and 9 -10% to get an idea of how much time in hand once turns 10%. Trouble is most batteries date from 2013 now. It can sometimes take a considerable time for flasher to even recognise N9 if battery on 0%.Trying to boot with depleted battery takes several % of SOC out of it.

Unfortunately can't offer you solution here, but are these genuine OEM housings or copies? I always use fine spudger to detach front camera from housing as junction of cable strip to camera seems quite fragile.

About the only issue with my many N9 resurrections is increasing incidence of emac failure, but at least a source of spares. Majority of "dead N9" are just 0% battery so flashing to ~ 10.5% SOC then connect to charger to complete. Only ever had one which wouldn't take the Swiss firmware Swiss DFL61_HARMATTAN_40.2012.21-3.480.04.1_PR_LEGACY_480_ARM_RM-696_PRD_signed.bin

Good luck!