I recently bought a Burgman ( coming from a SYM Joyride ) and haven't used it yet . The Battery took two weeks to go from working to dead and when fully charged it doesnt reach 12v . So the expenses start

Thing is the battery I took out is a YTZ14S and looking at replacements , they are suggesting YTX9-BS . Does anyone with a K9 AN400 know which I should be getting? Or knows if I can use either?
Cheers
gump