The isobutyl cation spontaneously rearranges to the tert-butyl cation by a hydride shift, is the rearrangement exergonic

Question:

The isobutyl cation spontaneously rearranges to the tert-butyl cation by a hydride shift, is the rearrangement exergonic or endergonic? Draw what you think the transition state for the hydride shift might look like according to the Hammond postulate.