Do you have the "Update" on your memory stick?, your going to need the "Update" on your memory stick for the battery bypass to work. Download the latest Sony firmware here:6.60 OFW - Downloads - PSPMOD.com - PSP / PS Vita Forums, now go to your "GAME" folder on your memory stick and create a new folder inside the "GAME" folder and name it "UPDATE".
Place the EBOOT from the link I provided into the "UPDATE" folder you created and then go to your XMB. What you want to do is find the 6.60 Update on your memory stick and before you press X, press and hold the Left Trigger and Triangle. While still holding the Left Trigger and Triangle, start the update by pressing X. When it says press X to install, you can now stop holding the trigger and triangle and continue with the update