eletic shift problem

Ok i got a 2011 irs 420 it sat up for a few months while i was working on it i ended up takeing the battery out to put in my oawpaws 350 cause his went out well when i got it back up and going i noticed that it is shifting from 3rd to 5th and sometimes it gets stuck and give me a – without me shifting it can a bad battery conection be the problem cause i had to tightrn them up one day and it started working right then all of a sudden it started acting up its not throwing a code are nothing and i have a 32% gr but that seems to be working good