Senator Nick Xenophon has warned the Abbott government its "dumb" budget is toxic with a key component of the Coalition voter base.

"This has been called the toughest budget in decades, but it also seems to be one of the dumbest," the South Australian independent wrote in a budget appraisal.

"The 'Howard Battlers' that re-elected John Howard on four occasions won't cop these changes."

Senator Xenophon is one of eight crossbenchers who will hold the balance of power in the Senate from July 1.