Increasing the MAH Will only Increase the Life Time the battery last after a Good Charger Increasing it Will not Effect the Performance or Damage the Laptop. But Be sure to Get one that would Fit the Laptop Higher the Mah Longer Time you use the Laptop, Lower the Mah= Lesser the time you use the laptop.
If you are buying the Battery off ebay please make it a point to get a good one as the laptops use a 3 Cell Lipo Battery that Provieds 11.1v.
If you need to know how dangerous Lipo is Type "Lipo Fire" in Youtube.