In Advance Wars
CO Powers debuted in Advance Wars. Each CO had one power each. Powers built up as units took and inflicted damage. Each CO Power meter was worth a certain amount of damage, with damage sustained being worth half as much as damage inflicted.
As well as a set of unique effects per CO, activating a CO Power also gave every one of that CO's units a 10% boost in firepower and defence. This boost is known as the "standard boost".
In Advance Wars 2: Black Hole Rising
CO Powers returned in Advance Wars 2: Black Hole Rising, mostly unchanged from the first game. However, a second tier of power was introduced: the Super CO Power, which were similar to the normal CO Power but stronger. Also, the way how full a CO's bar was measured was changed - rather than a bar that looped around the income and CO portrait, a series of stars was used. This made how much CO power meters were filled much clearer, as each star was worth 9 000G of damage.
The standard boost was changed slightly, and was only worth 10% more defensive strength.
In Advance Wars: Dual Strike
Advance Wars: Dual Strike changed the formula slightly again. Rather than making stars represent a monetary value, each unit was given a rating of how many stars it was worth. A third psuedo-tier of powers was also introduced: the Tag Power. A Black Hole idea, Tag Powers allowed two Super CO Powers to be used back-to-back in a single turn. The first CO would initiate the Tag Power and use their Super Power, then play their turn as usual. After they had finished, they would select CO Swap from the menu and each unit would get a second turn, under the effects of the second CO. On top of that, an attack modifier was applied depending on how well the two COs got on in the story.
The standard boost was returned to how it was in Advance Wars.
In Advance Wars: Days of Ruin
The entire way COs worked in general was changed for Advance Wars: Days of Ruin. In order to use a CO Power, first a CO had to be deployed onto a unit in order to use their CO Zone. Whenever a unit did 5 000G worth of damage, the CO's meter filled by one rectangle. When five parts were filled their CO Zone increased by a one square radius, then by another one square when their meter had all ten rectangles filled. Also, the CO unit could end its turn in order to use a CO Power. As well as an effect, CO Powers also gave the CO Zone infinte range for one turn, but completely drained the CO meter.