It is possible that the notifications are generated by the status area applet. You can disable this applet by moving the files

/usr/lib/hildon-desktop/status-area-applet-battery.so
/usr/share/applications/hildon-status-menu/status-area-applet-battery.desktop

To another location, and editting the file /etc/hildon-desktop/status-menu.plugins, commenting out the lines

[status-area-applet-battery.desktop]
X-Desktop-File=/usr/share/applications/hildon-status-menu/status-area-applet-battery.desktop
X-Status-Area-Permanent-Item=Special-Item-1
X-Status-Menu-Position=1