Is it required for a Battalion Commander to be present at a soldier's promotion ceremony to SFC?

There is nothing in the Regs that states that but if I was on the Promotion Line and they were pinning E7 on me I would request my Highest Ranking Officer to hold that ceremony.

No it is not a requirement. Traditionally, because the BC is the signature authority on the orders, they are invited/informed when the ceremony is.

Just thought I'd ask something as it seems like maybe the tradition has changed since I was in. The E7 and above promotions that I attended were not done in front of a unit formation (company or battalion) but rather were done more like the way a field grade officer promotion was done. That would be in a conference room or large office space; the appropriate level commander would "MC' the ceremony, speaking about the NCO, his background and achievements, introduce special guests like parents, spouses or children in attendance. Then he would invite whoever the NCO wanted to pin on the rank (usually spouse, parent or a particular officer the NCO had worked with, or the Bn Cdr) up to the front, and announce "publish the order"; the S1 would read the order, the rank is pinned on, and then the NCO would give a little speech.

Is it more common now to do it in front of a formal formation, sort of like the way a change of command ceremony is held? I'd never seen one like that for a senior NCO promotion so I'm curious about that.

First note is that I'm surprised that the CSM hasn't already been deeply involved on what happens with Senior NCOs promotions in his battalion. But to answer your question, the soldier usually has the biggest influence on who does the promotion. I would think the BN Cdr would be - and SHOULD be - there even while not "required" to be there by regulation.

As an old HHC Commander I offerred promotions to the CG. If he wanted he did them, otherwise I did them. As far as time/place of formation unless otherwise directed I decided that.

It is the current commanders choice, but in good taste you would be right to invite your chain of command, and if they decide to attend then you would work with their schedule. Just common curtesy.

No -- this is definitely NOT a requirement, I can assure you of that.

I actually leave the date up to the person that is getting promoted it is their promotion/Day. That way they can arrange the best time for their families to be there. There is no set protocol. As a BN Commander, I always try to be at a promotion regardless of rank, but I believe that the promoted soldier's desire for their family to be present trumps my schedule.

As you have already seen in many of the responses, there is no actual rule. I cannot tell you what to do but I can tell you what I do in my battalion. Because of the significance of the promotion from SSG to SFC (officially recognized as a Senior NCO) we ask the Soldier when they would like to have the ceremony in order for their family and friends to be present. I also ensure that the Battalion Commander is aware of the ceremony so that he can be there as well. It is that important. Myself and/or the BC do not have to do the actual promotion, they can have whomever they desire pin them. The promotion certificate is signed by the BC though and presented to them at the ceremony.
Personally if I were you, I would ask you CSM what it is he/she wants in conjunction with the soon to be promoted individuals. Maybe the CSM has a personal preference in these matters.

There is nothing in writing, but it always looks good if the BC or CSM are available to be at a Senior NCO's promotion.