5/5 would be used, in my mind to show PROGRESS, regardless of wins and losses
You have completed 3/5 battles today. Lose next two and it would read 5/5.
BUT if you are trying to show WINS vs LOSSES then it should read
Today I went 5-0, or 3-2, 4-1, etc. With WINS coming before the hyphen and LOSSES after.
Of course, that could be a purely American mechanic, in which case pardon my international ignorance!