By one definition, battle metal is a fusion of melodic death metal and Power Metal. The guitar parts are reminiscent of Iron Maiden's harmonizing, rhythmically complex duets, which took on a new meaning with bands like Carcass, In Flames, Arch Enemy, At The Gates, and Dark Tranquillity. The vocals and song arrangements, on the other hand, are more akin to Stradivarius and Sonata Arctica.
By the other definition, battle metal is a subgenre of black metal, closely related to epic metal and drawing on themes of medieval or fantasy battle and fighting, and in the opinion of some would be suitable for the soundtrack for a Role Playing Game. Battle metal bands like Summoning were (falsely) rumored to be possible contributors to the soundtrack of the Lord of the Rings movies, but this was mainly because of the Tolkien-related content of their music, but they did not appear on the soundtrack.
The band Bolt Thrower is considered to be a pioneer in this genre, as their name comes directly from a gigantic crossbow-type weapon used in the popular tabletop strategy game Warhammer Fantasy Battles. The lyrics and artwork of their second and third albums were based on the Warhammer game, as well as its futuristic companion Warhammer 40,000, with much of the art even being provided by the game's publisher, Games Workshop. The general theme of their lyrics is war and its consequences.
Most bands who play battle metal also contribute to other sub-genres of black metal: for instance, Bathory are prominent in the Viking metal sub-genre, and Waylander are pioneers of three sub-genres of black metal: battle metal, folk metal and Celtic Metal. Other metal bands have produced individual songs that fit the battle metal genre - the power metal band Thy Majestie is an example.
The band Turisas is considered to be the band who gave the genre its name by mixing all the previously mentioned styles and much more into one on their album "Battle Metal" (2004), even though Bolt Thrower has been together and performing since the mid-1980s.
Not to be confused with Australian War Metal.