The text says:

"BC overload ship capacitors may only be activated once per day, but also increase the void shiled's Stenght by 1"

Does the +1 add permanently to the Void Shield's Stenght or only for the single use reactivation?

it might need to be FAQed but my interpretation is that it is for that one round, the illogical logic is that the overload system bleeds the extra energy into the shields reinforcing them and that is how it gets rid of all the extra energy. At least that is how I would explain it in game. An Energy Spike that reinforces the shields when they reactivate and is lost as shields stabilize.

But that would make the Best Craftsmanship version worse than the Good Craftsmanship version, IMHO.

For example (let's suppose we have a Cruiser with Void Shield 2)

Best Craftmanship:

You have Void Shields 2 against the first Macrobattery in the salvo and Void Shield 3 against the second Macrobattery.

It only works once per day.

Good Craftsmanship:

You have Void Shield 2 against the first Macrobattery in the salvo and Void Shield 2 against the second Macrobattery.

It works three times per day.

RESULTS:

BC hits absorbed per day: 3

GC hits absorbed per day: 6

What book is this equipment in?

Zarkov N said:

Hostile Acquisitions, it's a Ship Upgrade.

The way I read it, the best quality version increases your base shield rating by one, in addition to allowing you to reignite the shields once per combat.

Errant said:

Yes, that's how I read it as well. The Best Craftsmanship version wouldn't be worth buying otherwise.

Following my above example:

The Cruiser permanently increases its Void Shields to 3, and re-activate them once per day while under a salvo.

Maese Mateo said:

I definitely read this as "Best Craftmanship overload shield capacitors may only be reactivated once daily, but also increase the void shield's Strength by 1." Emphasis mine.

I take from this that in in spite of only being reactivated once per day, it confers a Strength increase on a permanent basis.

This makes even more sense if you read the preceding passage: "Good Craftmanship examples provide additional reserve power for the void shields and may be reactivated three times per combat."

Not only does it not state a duration for the +1 Strength bonus (suggesting that there is none) of the Best Craftmanship version, but also if that bonus was not permanent, the Good Craftmanship version would be functionally better in every sense of the word.