To persist in prayer and not give up does not mean endless repetition or painfully long prayer sessions.
Always praying means keeping our requests constantly before God as we live for him day by day, believing he will answer.
When we live by faith, we are not to give up. God may delay answering, but his delays always have good reasons.
As we persist in prayer we grow in character, faith, and hope.
Luke 18:1 One day Jesus told his disciples a story to show that they should always pray and never give up.