How much stronger is a cannon battery than a single cannon?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
More than double the single cannon's contribution, because a battery removes the piece's biggest limitation. One cannon's threat depends on a screen it does not control and that can vanish; a stacked pair supplies its own screen from within the formation, so the rear cannon's threat is reliable in a way a lone cannon's rarely is.
What actually changes with two
A lone cannon's threat can be switched off by removing whatever piece happens to be its screen. In a battery, the front cannon is the screen, and removing it means capturing a defended piece, which is a far higher price than simply moving a pawn out of the way. That reliability is most of the extra strength.
Where the formation tops out
Against the enemy general specifically, a defended battery on the general's own file is close to unstoppable, the same principle behind 馬後炮 using a horse as the screen instead of a second cannon. Away from the general it is simply a strong, hard-to-dislodge attacking unit rather than an automatic win.
Related questions
Is a battery always better than two cannons on separate files?
Not always; see splitting cannons across files for when the alternative is stronger.
How many moves does a battery typically take to build?
Usually three or four, since the second cannon has to travel to the right file, giving the defender that many moves to prepare.
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