Interesting question. Here's a what if....
Say the battery only charged to 8 volts, would the starter then try to draw 150% of its normal current and blow the fuse link? I don't know. More research on voltage/current relationship of dc motor required.
Edit: Maybe I have that inverted. It may be if the battery over charges to 18volts, then the starter would draw 150% of it's normal current.