Step Up or step down converter need 5V

[Max A. (max_mma)]

Hi I need 5V 12A. I am not sure if I should use a 7.2 Li Ion Akku with 
6000 mAh and 30 A Output and step this down with some Stepdowns. The 
problem I read is that a little voltage drop of 2.5 V isnt perfect for 
converter.
Or should I use 3.6 Li Ion and convert them up with a boost converter?
Or do you have some better ideas?
This construction shouldt wheigh more than 500g
Thanks