I think this is a general question, not quest-specific at all and maybe I missed a discussion but I haven't seen this mentioned so I'll ask and see if anyone else is experiencing this.

In my first game, I'd equip my followers Lydia and Argis with a soul-trap bow or axe and soul gems and they'd be able to soul-trap the same as I could. After patch 1.4 in my second game, Lydia and Argis could no longer do this but they could before the patch. I've just gone back to my first game and Argis can still soul-trap...so maybe that second game is bugged? Is anyone else having any problem with this or are your followers still able to soul-trap? Thanks!

Check their Weapons, I think they can get discharged.

I've noticed with some weapons that have soul trap, if they are enchanted with a grand soul gem they never run out of a charge. It might be because I'm using a daedric war hammer. Because they have a daedra heart to make them, they never lose a charge. Try daedric weapons!

I think only Fiery Soul Trap works for followers. I read it somewhere in uespwiki

In both games I believe I charged exactly the same way...just plain soul-trap. I'd have to test that but what it sounds like is that everyone else is still able to have their followers do soul-trapping so that helps a lot. I always keep their weapons fully charged so there's no chance they'll throw them away when empty. Not sure what's going on with that #2 game but I'll make note of what I use to enchant and see if it happens again...glad to hear it'll still work though! Thanks.

Fiery soul trap?

Followers don't throw their weapons away do they? I haven't noticed this, I do take their weapons and constantly recharge them though.

Wow, no matter what I've given my followers, they have never soul trapped anything. I didn't know they could! (Gave them a soul-trapping weapon and lots of soul gems of all sizes, and no go.)