I've always heard all new batteries should be charged at a low amperage on an automatic charger overnight. AGM batteries require a special charger, but it sounds like you have that covered.
Throwing a low charged battery in your car and relying on your alternator to charge it is very hard on your alternator's bridge diodes.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 3.73s
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3600 stall lock-up converter and 3.91's (closest thing to an automatic 5 speed going)