The origin of the idiom "losing battle" is related to the idea of a battle or conflict that is being fought at a disadvantage, perhaps due to a lack of resources or unfavorable conditions. The phrase has been in use in English since at least the mid-19th century, and it has been applied to a wide range of situations, including personal struggles, political campaigns, and military conflicts. In general, the phrase is used to describe a situation where success is unlikely, but where the effort to achieve it is still considered worthwhile or noble.