Can using the first ability cause the second ability to trigger?
[Source: WotC]
Yes. If the upgraded character defends and would take an even amount of attack damage, instead it takes no attack damage. That causes the second ability to trigger. You usually get only one use out of the Emergency Defense Field.
If I have Emergency Defense Field and
Recon System attached to my character, and it’s attacked, can I choose which battle card to scrap (Recon System) after both player’s cards are flipped, to try and trigger Energy Defense Field?
[Source: WotC]
Yes, you can choose which card to scrap. The attacker always flips first, then the defender. Since you’re defending, you’ll know what the attacker flipped when you have to decide for
Recon System.
Dreadwing is equipped with Forcefield, Emergency Defense Field, and
Backup Bag takes 5 or more attack damage, what happens? I think that the Forcefield would try to scrap first (reducing the damage to 4) and the Back-Up Bag would save it... then the Emergency Defense Field would make Dreadwing take no damage and scrap. Is that right?
[Source: WotC]
That is correct!
If a card with a 'When this battles…' trigger (e.g.: Emergency Defense Field ) is played on a character after the attacker is declared, will the "When this battles…' ability work?
[Source: WotC]
The trigger for all "when this attacks/defends/battles" is at the same time and happens only once as the attacker is declared and tapped. If you use a "when this battles" trigger on a character to then play a "when this battles" upgrade onto that character, the upgrade won't trigger as it's now too late in the attack for those effects to trigger.