Sorry if this has been asked befor. The BSG for huge ships, how many shield points can you get back at end of turn? Is it only 1 or can you get 4 back if you have 4 energy to use?

Just one. This falls under "abilities trigger once per opportunity".

There's that and the limits imposed by the card's wording. It says to spend one energy to recover one shield. The only other way around it would have been by having multiple copies of the card, but because it's "Limited", you can't.

If you were able to recover more than one shield, the card would probably be worded like "You may spend energy tokens to recover one shield per token (up to your shield value)."

But it doesn't, therefore, you can use it once only at the end of each round to recover one shield, and you can only have one BSG.

My question is maybe a simple one... But where do you spend the energy point from? The ship itself or can you spend an energy you have already placed on a weapon ?

My question is maybe a simple one... But where do you spend the energy point from? The ship itself or can you spend an energy you have already placed on a weapon ?

You spend it from the ship itself. Energy tokens assigned to upgrade cards can only be spent for the effects of that specific card.