Jango Fett is armed with twin WESTAR-34 blaster pistols:
These weapons are quite small and I don't see any place to insert a power source.
Its standard issue power cells carried energy for 100 shots however the rifle could also be loaded with plasma cartridges that could last for more than 500 shots.
Indeed there seems to be plenty of room on the E-11 to place a power cell or plasma cartridge:
(I believe the power cell is the near-white, square protrusion from the middle of the E-11 shown above.)
Where is the power source for the WESTAR-34 blaster pistol? Does it acquire power some other way? How many shots can be fired before reloading?