NZ PM Ardern Announces Shock Resignation

The speaker reflects on their years of leadership, highlighting the privilege and challenges of leading a country. They announce their decision not to seek reelection, citing a lack of energy to continue effectively. Despite facing numerous challenges, including a pandemic and economic crisis, they express pride in their achievements and confidence in their successors.

What does the speaker mean by having 'a full tank plus a bit in reserve'?

How does the speaker feel about their achievements over the last five years?