In the light of other comments, my two penn'orth ...
On the length of battles: I take
@Rico's point about people losing interest with long battles (especially team memebrs who are perforce sitting out that "turn"): but, I also dislike battles with too short a timescale to reasonably achieve the given objectives ... IRL you cannot do much in 40 minutes, especially if someone shoots at you whenever you move ... if the battles can be no longer than 40 minutes, then they need to be on small maps and with small forces (relatively speaking);
I also favour "vanilla" units: e.g. Pz IV being the default Axis tank equipment, with perhaps one (small) unit of Tigers or Panthers on the whole "front" for selective use by the OC at the decisive (he hopes) moment ...
I'm not a fan of too many "meeting engagement"-type battles, with equal-sized forces stumbling upon each other and both attacking to seize the same objective. The battles need variety to keep players' interest, but IMO should be based on the premise that attackers have (or think they have ...) an advantage over the defenders, and whichever way the background storyline is set up (Russian offensive, German counter-offensive, etc ) one side or the other should be working generally on either an offensive or defensive premise, and have their objectives and VLs (and forces) structured accordingly.
Hope this is helpful, and not just illustrative of my prejudices!