There are numerous fraudulent SDHC cards offered for sale on the web etc. so unless you purchase directly from the manufacturer they need a comprehensive test of their capacity and performance. Put the SDHC card into a USB dongle and test it. For those having to use MS Windows the below is a good test and will take a time to complete its tests.
Test for Fake USB Flash Drives – H2testw
H2testw is a free tool that can be used to test for Counterfeit or Fake USB flash drives, and check your USB Flash Drive for errors. It works by filling the chosen target drive with test data and then reads this data back to verify it. You should probably copy your data elsewhere before performing this test on the USB Drive, or you could risk losing data.
Authors Website:
http://www.heise.de/software/download/h2testw/50539
It has the option to run the program in English.
Richard