G. , or Gold, is the currency used to produce units and buy battle maps in the Advance Wars series.
During a battle, a player earns G for every property they own at the beginning of a day. This G can be used to produce new units, and some of it is also used to repair damaged units that are on a friendly city.
Except in Days of Ruin, a player earns a certain amount of G for every battle completed in Campaign mode and in the War Room. This G is used to buy new maps and COs from Hachi in the Battle Maps store.