Matt Ward, heh....what a douche. If for some reason you are Matt Ward, no offesnse. But I do hate your work.
But seriously. I don't own all 40k manuals ever released, but several dozen novels make reference to lances as being very specific and different from batteries. There are macrobatteries, plasma batteries, laser batteries, missile batteries, probably even a couple others I can't remember. But lances are pretty specific; I can't find a description near me other than my rogue trader books, which define a lance as having a massive plasma/battery based energy supply, and dozens upon dozens of specifically designed emiters and refractors generally mounted upon a turret. This creates a piercing beam of energy that rapdily cuts through any known ship armor, but inflicts little damage potential compared to betteries. This is very similar to BFG, where batteries usually have superior damage potential to lances, but are not nearly as reliable to actually inflict damage. The only races I know who don't follow this very specific description of lance are the necron and the tyrranids, who either use biological equivalents or some warp based shenanigans. The Rak'Gol are another exception, and they use extremely powerful beams of radiation to achieve the same effect.
Admittedly, I can see where laser based batteries like a sword class frigate blur the line between the two, but that is pretty much the only one. In every thing I have read, lances are used for precision targeting to destroy specific vulnerable enemy elements, bombardment cannon are souped up magmabombs used to destroy large areas and soften up an entire infrastructure before assault and nova cannons are also used in orbital bombardment; thing is, they are hard to position and only for systematically wiping out/cleaning continents, like a poor man's cyclonic torpedo most of the time. They can even destroy the planet itself, given time. All these descriptions are against ground targets, obviously.
