hat has never been the rule and I doubt it will become the rule in 2010. 273.5 requires a cohabitant relationship and the infliction of injury causing a "traumatic condition" that is a
condition of the body, such as a wound or external or internal injury, whether of a minor or serious nature, caused by a physical force. You should note the language "whether minor or serious nature."
243(e)(1) applies to a battery inflicted on a cohabitant. A battery can be any offensive touching or more but this statute does not require an injury resulting in a traumatic condition.
Penal Code 273.5 is inflicting "a corporal injury resulting in a traumatic condition" on your "spouse, former spouse, cohabitant, former cohabitant, or the mother or father of [your] child,"
While most traumatic conditions are visible injuries such as bruises, it is possible to have very serious internal injuries that may not be immediately visible.
As you have noted, Penal Code 273.5 is a "wobbler," meaning it can be charged as a misdemeanor or felony. Although some District Attorneys have office policies that provide guidance in charging, there is no law defining the difference between a felony and a misdemeanor.
The District Attorney has discretion whether to charge a felony or misdemeanor when the initial complaint is filed. The judge can then has discretion to reduce a felony charge to a misdemeanor at the preliminary hearing, at sentencing, or even after probation is complete.
As Mr. Kaman notes, Penal Code 243(e)(1) does not require injury. The class of protected persons is also broader; in addition to those listed in 273.5, it includes "fiance, or fiancee, or a person with whom the defendant currently has, or has previously had, a dating or engagement relationship."
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.