It's Acer. What did you expect? The main problem battery packs suffer from is that some cell won't keep up with the rest. Unless the pack has a forced balancing system then when that cell gets low the other cells will back-drive current through it doing some damage and lowering the life. There is usually some battery management chip that is looking for current-in vs current out vs voltage and it is adapting the usage reporting on that basis. I had a battery that was reported as 100% charged and offered less than 5 minutes before the computer could not run.