Ohmmu Sodium Ion 12v Battery

Installed an Ohmmu Sodium Ion 12v battery yesterday...perfect fit and weighs 1/3 of the original one. I notice though, it's doing what the stock battery was doing before I changed it. Going from 13.5-14v parked or idling along and then after several mins of driving on the highway it creeps down to 12.5-12.9 then back up again when parked. Is that normal? There should be nothing draining it while driving (unless it IS my ABS pump cycling more than normal from my other thread). Anyone with electrical knowledge please feel free to give your advice or experience.