Hammer S battery issues

scorpion

\n\nMy Hammer S has started having battery issues.
It works fine until around 30% but then the battery falls rapidly within minutes and it shuts down.
Although the phone is only 8 months old, I presumed the battery was at fault so purchased a new (genuine) UMI 3200mAh cell but it still has the problem.
I then tried a factory re-set and ran it with only stock apps after performing the advised battery 'callibration' but again, at 30% it starts to fail.
Is it worth re-flashing the ROM in an attempt to fix the problem, or would that be no different from a factory re-set?

Looks like I've fixed it.
I did another wipe data / factory reset from recovery mode and not using Android (Backup & reset), also wiped cache partition.
Both batteries now working as normal.