I have been using Yuasa on most of my bikes not just Hyosung , i trust them. I’ve had a yuasa last me 3 icy winters (3yrs) and it was also because the charging system was in good spec (Stator = good AC output , Reg = good DC output)
UniBatt & VARTA are also good alternatives because i have used them also.
MotoBatt ,i’ve not tried them either as per simon, (but i don’t have a desire to try them now though)
14-BS is correct and OEM size as per good Simon!