I am trying to create a robot that has 2 12v motors with a 5A stall current. For my other robot project I used a large 12v lead-acid battery to power the whole thing. However, my new robot is much smaller and will need a smaller power source. After doing some research, most people recommend either getting a setup of 8AA or 10 rechargable AA batteries to power it. I was wondering if this is the best option, or if using something like a 7.2v battery pack with a voltage step up regulator would be better for this project. I'm just wondering whether the efficiency loss from the step up would be worth it compared to just getting a bunch of AA batteries.
If it were me, I would consider running LiPo packs with a voltage regulator to get the voltage you need.
A 3s pack starts out at 12.4V charged and ends at 9V discharged. If you can live with that range, the powering your motor drivers directly from the 3S LiPo should do you well. Then get a regulator for your Arduino and you are good.
Hobby king has much of what you would want if you go this route. Here is a charger that will charge 3S batteries. About $12 Here is an inexpensive LiPo battery, 3000mAh capacity. But they have a zillion, larger and smaller.
If you NEED 12V, add more cells, maybe even put 2 3S packs in series to get a 6S pack (24V) and regulate that to 12V for your motors.
I did not see a cheap regulator that gives 12V out and provides enough amps for your needs though.
How much run time do you want? How much space is available?
I don't think rechargeable AA batteries can put 10 amperes.
Some can, trading in 25-50% capacity.
3S Li-Po would be my choice, though.