Minor winter battery issue

New battery, drove the car the previous day parked it at home and got in it late this afternoon and it didnt turn over, meanwhile the battery is fully charged at 13v, what i did was disconnect the positive then put it back went in the car and it started fine, my question is why will the car not just hold the charge initially. what made it start after reconnecting the battery, is there any symptoms here that stick out to anyone or i should get to checking, input would be nice thanks!

I suspect that when you originally replaced the battery, your terminal was not properly secured. This allowed sufficient current to start your car, but if it loosened some more after driving around, it did not allow enough current to turn the car over. Reconnecting the battery probably resolved the issue. Just a guess but if you search, a loose connection is a very common cause for starting issues.