mercruiser 170 224 slow cranking

its a 1985 mercruiser. thought the battery was no good so bought a new one w/750 cranking amps. still slow cranking w cranking starts and stops and the wires at the battery start to get hot. could it be a starter motor? Anybody with any idea..Thanks

 

check connections at the battery (both sides)then check connections at the block grounds included if going past an assist soliniod make sure these are clean too
if all this is good then look at the starter

 

Thanks