A Battalion wall was a pattern or shape put together from Lupari ships to protect planets from the Flux.
While the Lupari and humans were species bonding (TV: The Halloween Apocalypse), the Sontarans got behind the Battalion Wall in the milisecond before it was made and launched temporal attacks across time. (TV: War of the Sontarans)
The Sontarans made a plan to act like they are orginising a truce meeting with Daleks and Cybermen. First, they had to predict the exact space-time coordinates of the final Flux event. They planned to kill them and surround themselves with the Lupari shield and save themselves. (TV: The Vanquishers [+]Chris Chibnall, Doctor Who series 13 (BBC One and BBC America, 2021).)