Need help for my robot project


I need help in building my robot. I am using an arduino leonardo and an adafruit motor shield v2. I am also putting in an ultrasonic sensor. I am planning to make it small, so i am using the zumo chassis. That means it will function with the two micro metal gearmotors (also known as n20 gearmotors).

The zumo chassis has a place for putting 4 AA batteries. I want to recharge the batteries, and putting rechargeables means that i will only have 4.8v. But my project requires at least 6v. I need to power the two motors, the ultrasonic sensor, the arduino and the motor shield. So i will be needing a lot of current. At the same time, i need to fit the battery in the battery compartment of the zumo chassis.

Which battery should i use?
Should i use two li ion cells (thats about 7.4v and 2600mah)?
If i use alkalines, will it work?
Please help

Can't tell what your current draw will be, given the paucity of information you have supplied. That said, why not first try everything out with the supplied batteries. If it turns out you are 1.2volts short with rechargeable AA batteries, use 5 of them. Should be about the same.