I could be wrong, but how can you have percentage for bar chart? It only applies to pie charts. Best to just show your figures in amounts, then title the axis as Percentage so the reader knows what the figures represent. Other than that, there appears to be no feature to format the axis in this version (same problem for formatting amounts into currency with dollar signs and thousands separators, which there is also no option for).
The only solution I found for this was to create my own labels and overlay them.