Chapter 265, Section 13A of the Massachusetts General Laws creates the crimes of assault and battery and so-called "aggravated" assault and battery, which is assault and battery that is committed with three possible aggravating circumstances: A&B which causes serious bodily injury, A&B against a pregnant woman, or A&B against a person who has an abuse prevention order against the defendant.
There are no minimum sentences for any of these crimes. Simple assault and battery is a misdemeanor punishable by up to 2 1/2 years in the house of correction; the aggravated offenses are punishable by up to five years in state prison (if you are indicted and prosecuted in superior court) or up to 2 1/2 years in the house of correction (if the case is prosecuted in district court). The essential difference between regular A&B and an aggravated form of A&B is that aggravated A&B is a felony, while simple A&B is a misdemeanor. A felony conviction can have substantial effect on collateral matters, including your citizenship (if you are not a citizen), your ability to get or maintain a job, or your housing status.
If you have a serious prior record including convictions for violent offenses, the Commonwealth may indict you and prosecute you in the Superior Court, where you could be sentenced to time in state prison.
Speak to a criminal defense attorney immediately about your options.
There is no minimum mandatory sentence for aggravated A&B. On a plea, given your record, you are probably looking at a conviction, as opposed to a CWOF or some other non-conviction disposition, but you may not have any prison time imposed and could get probation. The actual sentence imposed depends on a variety of factors such as the facts of the specific case, prior record, injury to the victim, substance abuse, and mental health issues, just to name a few.
Best of luck,