Battlemagic Perception spell : Taking a free action outside one's turn?

[Shin Okada]

Battlemagic Perception spell from Heroes of Battle says,

This determination happens quickly enough that you can attempt to counter the spell as a free action.

At first glance this spell seems wonderful. But I noticed one thing. AFAIK, unless otherwise noted, a character/creature can take free actions only during one's turn. The only exceptions are speaking (per PHB 114), spells like Feather Fall which specifically says so, and such. And Feather Fall is changed to an immediate action spell after the introduction of Immediate action and swift action.

If so, allowing a counter spell as a free action seems to be not that useful. It is possible that the caster attempts a counter spell during HIS turn (say, when an opponent tries to counter his spell or use some immediate action spell). Otherwise, the caster still must ready an action (a free action is one of the options for readied action).

Am I wrong about the ruling of free action? Or shall I just consider Battle Magic Perception as an exception which allows a caster to take a specific free action out of his turn? Or shall I translate it to be an immediate action?

 

[Random Bystander]

Note: I do not have that book, so I will approach from the general case.

By RAW, unless it specifically says that you get a free action, you don't get a free action.
By RAI, if a spell, feat, or other rule would not work as written, but the intent is clear enough (ex: Ride-By Attack), then the solution is generally implicit in the rules.

That is, Ride-By Attack requires the character to be allowed to make a charge along a line adjacent to their target to work, therefore a fairly common fix is to allow such with ride-by attacks. If Battlemagic Perception "works" (does not violate RAW without written exception; is sufficiently capable; is self-contained; etc) as written, then it is likely that it does not give a free action. If, however, it needs that free action to be useful, then allowing it to grant that free action sounds like it may be the right choice.