I suggest the following:

Control: The user may make an Easy (π) Leadership check combined with the
Battle Meditation power check. If the user is able to activate the power
and succeeds on the check, he may send simple orders as part of the power. If you spent (Dark), you may use Coersion for this check instead, and the target cannot disobey without passing a Simple Disipline check.

Mastery: If the user did not use (Dark) to generate (force), choose one skill. While affected
by the power, each affected character counts as having the same number
of ranks in the chosen skill as the affected character with the most ranks
in the skill. If the user did not use (Light) to generate (force), each affected character may be the target of another force power- Ignore the other power's normal range and target restrictions.

This moves the "OMG MIND CONTROL" to a level where it's weakness is appropriate, and replaces it with an effect that's harder to pull off (needing all darkside instead of just 1 darkside), but is comparable to lightside's skill sharing. (It also replicates vader's comm screen force chokes- there's no reason it has to be a GOOD power you channel, just that you target an ally. )

Problem with the Control change is that Simple difficulty = no difficulty dice, and is pretty much a trivial check for a character to make. Using Coercion does seem fitting though. Perhaps change the upgrade's effects that each round/activation of the power requires an Average (2 purple) Leadership (light side) or Coercion (dark side) check to convey orders, and that if a target wants to try and resist, treat it the same as resisting a Force power per the sidebar on page 193.

The Mastery change for dark side makes zero sense though for the general sense of what Battle Meditation is. The way it's written, the character could decide to blast the targets with Influence or Unleash just as easily as they could use Heal.

Perhaps for the Mastery Upgrade, it'd just be easier to just let all targets do the "use best skill rating," but that if a dark side Force Point was used, then each target suffers 1 strain for each round they're affected by Battle Meditation, reflecting the mental toll on having a dark will push them forward and onward. And if no dark side Force Points were used, the targets instead recover 1 strain for each round they're affected to reflect the sense of encouragement the Force user is providing.