[JimD]

I am pretty sure it is not the lack of registration. It is more likely the battery was not fully charged when you got it. I always put a new battery on the charger just-in-case. They are typically charged but some have needed a few hours on the charger.

Lack of registration means the battery will be charged like an old battery but it would still receive charge. That would not change a battery from fully charged to discharged to the point it won't start quickly.

It could also be a defective battery. I bought one for my daughters car that had a hole in it. She wouldn't go back where she got it, of course, so I drove a couple hundred miles to figure this out and get it replaced. All I knew when I left was it worked imediately after she bought it but wouldn't start the car a week or two later.

Jim