Hard to start, slow turning over

Cranked it, moved it out of the shop, 10 minutes later it would not turn over. When it did crank it was slow to turn over. I bought a new battery. Stock was 14ah battery, I installed a 21ah battery. The motor still turns over slow. And sometimes will not turn over at all.
I’m at work for a couple weeks, when I get home I’m checking connections, battery frame ground, starter, starter contactor. I figured I might have a loose connection somewhere.
Has anyone else had this issue?