I have now bought the second battery for my DEFY (without plus!) First I ordered this battery because it was cheaper: Original Battery Replacement Battery Motorola BF5X Li-ion for Motorola MB525 Defy XT530 FireXT However, this was not recognized by my Defy and then also not loaded (discharged only)
This battery has been identified, charged and my Defy is now running as the first day.
little info: My Defy runs on a custom ROM (CyanogenMod)