Is it a must that the charge is recovered at the end of round regardless if you spent it or not?

Or can you leave it inactive and wait until the next round to spend the inactive charge to gain either a lock or focus?

You might have me blocked still, be here's this anyways. It is mandatory to recover a spent recurring charge since it is not a "may" effect:

END PHASE
The End Phase is the fifth phase of the round. During the End Phase, all
circular tokens are removed from all ships. Then, each card with a recurring
charge icon recovers one charge.
• After this phase, the criteria for winning the game are checked.
• If the game did not end, the Planning Phase of the next round begins.

Use of “May,” “Can,” and “Must”
The word “may” is used to mean “has the option to.” For example, an ability
that says “At the start of the Engagement Phase, you may perform a 󲁂
action,” means that the ship has the option to perform the action, but can
also decline.
The word “can” is used to mean “has the capacity to.” For example, an ability
that says “While you boost or barrel roll, you can move through and overlap
obstacles” means when a ship with this ability boosts or barrel rolls, it ignores
the rules that prevents them from overlapping or moving through obstacles.
The ship always applies this effect as the effect is not optional but instead an
expanded capability.
The word “must” is used to mean “is required to.” Although all effects that are
not “may” effects are mandatory, the inclusion of “must” is used to reiterate a
mandatory effect that could provide a drawback to the ship with the effect.