Anker Battery stops charging at 50%

I have an i9505 running resurrection remix 5.5.6 with alucard kernel. all was going ok-ish until I used the battery calibration app to delete the batterystats.bin file. since then the battery will only charge up until the high forties or low fifties in percentage terms. the battery was fully charged when I calibrated it, it's really getting on my nerves now.

could it be a kernel thing ? I have fast charge enabled in alucard...

any help would be appreciated !!!