the standard back won't fit completely over the extended battery on my phone if i try to use the bottom tabs to secure it. by removing those tabs it allows the back to rest flat against the battery, otherwise the tabs get in the way of back resting flat on the battery or they cause the back to bow out if you force them in place. the seidio surface case has lower tolerances to keep it slim so that little bit of bowing out of the battery door, keeps it from snapping together at the bottom of the phone. even with the bottom tabs removed on the standard battery cover, if you put the standard battery in the phone and close it up the back is still kept securely in place by all the other tabs. you also have the extended battery back as a spare if you need one. i have a case on my phone all the time so i wasn't really concerned about modding the standard battery door. those two little tabs were sacrificed for the greater good, a perfectly fitting standard case while using the extended battery.