I still think that a battle is most effectively, in 4e terms, an 'adventure' (or maybe an SC if its not as important). Various things happen, but its ENTIRELY PC-centric. If the PCs direct units in battle, then they make some checks, if they fight, they make some checks, etc. I wouldn't really bother with giving units of 100's of creatures combat stats. Certainly some unique enemies might show up and create a real combat encounter, the ordinary rules should handle it. OK, 40 orcs show up too, you can certainly call them '4 swarms' and throw them in there as well, that can be perfectly interesting.
I just don't see 4e needing a mass battle system. Obviously if you have a bunch of wargamers who WANT to play such a thing, by all means break out your Chainmail and go at it! This is a much more solid rule system than anything TSR has published in the decades since. However, I don't think such things mesh well with 4e, really. I would consider it sort of an 'other thing' that you did for the pure fun of doing that, and leave the RPG aspect aside.
Classic D&D was a bit more aligned towards that sort of thing being a part of the game, but I can tell you from personal experience VERY FEW entire groups of players are interested enough in mass combat to actually make it something you should use in a D&D game, except as backdrop. IME most of the players are bored by it, and it takes a LOT of time to churn through...