can i replace my own battery with an iphone battery without voiding warranty

No, you can't!

Apple doesn't sell parts to end users and this service must be done in an Apple Store or Authorized in order to be done with an original part, not to void warranty or to receive warranty for the service.

See iPhone Battery Replacement - Official Apple Support

Not only would you void any warranty or AppleCare agreement that was still active, you would permanently forfeit your right to have the device serviced by Apple or any authorized service provider.