Some AGM batteries come from the factory filled with electrolyte and charged, while others come with the electrolyte separate for the dealer to put in when the battery is sold. The first way is easier for everyone involved at the point of sale, but not necessarily better in the long run. Batteries self-discharge over time, and the longer a battery sits on the shelf, the lower its charge will be when you buy it. If it stays too low for too long, lead sulfate crystals form on the lead plates, a process called sulfation. At this point even a conventional recharge might not bring the battery back to health. The charge will come up initially, but after a couple of days it will drop back down to where it was. The better bet is to have the dealer add the electrolyte and put the battery on a charger for a while before you take it home so you start out with a fresh, full charge.