I sincerely doubt VEX would even consider releasing documentation for updating battery firmware, let alone encouraging people to do it.
First of all, the batteries can hold a lot of energy. If you don't know what you're doing, you might end up with a shock, explosion, or worse.
Secondly, I'm sure the batteries were not made to be serviceable (even though they may actually be fairly serviceable), and updating the firmware would probably require desoldering and a special programmer.
If any of you are commenting based on my post, do note that I said at the factory, not by end users.