If it's defaulting back to the original, you must be adding something that overwrites the dll containing the custom icons. Also check that your registry contains the following:
Code:
[HKEY_LOCAL_MACHINE\Security\ResOver\Bitmaps]
"BaseDll"="phcanOverbmp.dll"
[HKEY_LOCAL_MACHINE\Security\ResOver\Bitmaps]
"BaseId"=dword:00000000
[HKEY_LOCAL_MACHINE\Security\ResOver\Bitmaps]
"BatteryIconIdStart"=dword:000003e9
[HKEY_LOCAL_MACHINE\Security\ResOver\Bitmaps]
"BatteryIconLevels"=dword:00000065
Are you installing any custom taskbars? phcanoverbmp.dll contains the battery icons and the volume icons are either in htcvolumecontrol.dll or shellres.192.dll or shellres.192.dll.0409.mui (calk's).