[bkahl]

FRC legal batteries are sealed to allow for use in any orientation. If we were only allowed to charge upright, wouldn't we have to place batteries in the robot upright too?

However, we brought this up to our battery distributor. Their advice was to store batteries upright if they were being left for a long period of time. While it is a 'sealed' battery, it will leak if inverted or left on its side for too long.

TL;DR.... It doesn't really matter unless you leave your batteries in inverted or on a side for a long period of time.