EMOTIONAL SPECTRUM: WILL: If the Power Battery, attached Power Ring, and Constructs are all the same color, each opposing character may be given no more than 1 free action per turn.

DUO ATTACK
Give this character a power action. This character makes 2 combat attacks (close and/or ranged) as free actions and possesses during this action.

MULTIATTACK
Give this character a power action. It can be given any 2 actions as free actions. This ability can’t be countered.

Does the Green Lantern Power Battery:

1. shut down opponent's Duo Attack? I believe, YES.

2. shut down opponent's Multiattack? I believe, YES - the battery isn't "countering" the ability, just negating it.

You are correct on both accounts. The Power Battery prevents opposing characters from taking more than one free action per turn period. As of now, nothing gets around this.

It doesn't shut them down entirely, the acting character still can do the first free action but can not take the second.

So you should just not use Multi-Attack or Duo Attack (unless you get some sort of bonus from your first attack in Duo Attack). Essentially shutting it down.

thanks - which is what I meant by "shutting it down" - you would get one attack (free) and then ... nothing more.