It will be compatible - have look at your current battery, its probably a yuasa ytx BS 12 or very similar?
There is a table which shows what the Motobatt MBTX12U replaces
HEREI admit to being a bit personally prejudiced against Motobatts as one failed on me, but it could happen to any battery! Just make sure it has the same terminals/posts, is the right size etc.? Why doesn't he want it?