I have units at a battlefield at the start of the turn, my opponent moves my unit off the battlefield to my base, the battlefield is empty, they then charms my unit back to the same battlefield, do I get a point for conquering?

No, you do not get a point for conquering the battlefield in this scenario if you have already scored it during the current turn.

According to Rule 447: "A player may only Score, from either method, once per Battlefield per turn."

Even if your unit was moved away and then returned to the battlefield via Charm during the same turn, the restriction on scoring remains. If you already held the battlefield at the start of your turn or had already scored it through another method earlier that turn, you have already exhausted your scoring opportunity for that specific battlefield for the duration of that turn.

Key points regarding this interaction:

• Scoring Limit: You can only score each battlefield once per turn, regardless of whether you score via Hold (at the start of your turn) or Conquer (by moving a unit there).
• Conquer Definition: Per Rule 446.1, a Conquer is defined by gaining control of a battlefield you have not yet scored this turn. Since you have already scored that battlefield this turn, moving a unit back onto it does not qualify as a Conquer action for the purpose of scoring.
• Timing: As noted in FAQ #7486, you cannot gain points by moving a unit away from and back to the same battlefield on the same turn. The only exception is if you were to move to a battlefield and conquer it during your opponent's turn (using an ability like Ride the Wind), as that would constitute a different turn.

Note: I could not fully verify this ruling against the retrieved rules, as the outcome may differ if the interaction occurs during an opponent's turn where the battlefield had not yet been scored.