Either a YTX14-BS or a YB10L-B depending on the model.
PIAGGIO X8 125 Premium Euro 3 125cc
PIAGGIO X8 Premium 125cc
PIAGGIO X8 Street Premium Euro2 125cc
You really need to check the model number on the old one before you order anyway, just to be certain. If you don't have the old one, you should be able to get a good idea of what fits by measuring the width, length and height of the battery holder.
PIAGGIO X8 125 Premium Euro 3 125cc
PIAGGIO X8 Premium 125cc
PIAGGIO X8 Street Premium Euro2 125cc
You really need to check the model number on the old one before you order anyway, just to be certain. If you don't have the old one, you should be able to get a good idea of what fits by measuring the width, length and height of the battery holder.