Returning Time Difference As Days/ Hours/ Minutes

I have written a function that returns the number of Days, Hours and minutes from a given number of minutes. On testinf the results are close but not quite there. Can anyone see where I have gone wrong or is there an easier way of doing this? Code is as follows:

CREATE FUNCTION dbo.GetTimeBetweenLong
(@StartTime DateTime, @EndTime DateTime, @CurrentDate DateTime)
RETURNS VarChar(50) AS
BEGIN
DECLARE @TotalTime Numeric
DECLARE @Minutes Numeric
DECLARE @Hours Numeric
DECLARE @Days Numeric
DECLARE @MinutesInDays Numeric

IF @EndTime IS NULL
BEGIN
SET @Days = DATEDIFF(Day, @StartTime, @CurrentDate)
SET @Hours = DATEDIFF(Hour, @StartTime, @CurrentDate) - (@Days * 24)
SET @Minutes = DATEDIFF(Minute, @StartTime, @CurrentDate) - ((@Days * 24)*60) - (@Hours * 60)
END
ELSE
BEGIN
SET @Days = DATEDIFF(Day, @StartTime, @EndTime)
SET @Hours = DATEDIFF(Hour, @StartTime, @EndTime) - (@Days * 24)
SET @Minutes = DATEDIFF(Minute, @StartTime, @EndTime) - ((@Days * 24)*60) - (@Hours * 60)
END

IF(@Days <0)
BEGIN
SET @Days = @Days - @Days - @Days
END

IF (@Hours < 0)
BEGIN
SET @Hours = @Hours - @Hours - @Hours
END

IF (@Minutes <0)
BEGIN
SET @Minutes = @Minutes - @Minutes - @Minutes
END

RETURN CONVERT(nVarChar(10),@Days) + ' Days, ' + CONVERT(nVarChar(5), @Hours) + ' Hours, ' + CONVERT(nVarCHar(5), @Minutes) + ' Mins'

END