There are plenty of batteries out there that can do that, it all depends on what you want done within the system. Fans are not incredibly complex, but their power draw and how much power they use is something you will learn over time. Where the stuff gets a little more crazy is when you try to link up various different battery types to a system. LEDs generally will not function if under voltage...but if over voltage most electronics will fry. 4 AA batteries linked in a series can have a different voltage depending on if they are Alkaline, Nickel, or Lithium. Knowing what battery type you can use is pretty critical before going out and buying batteries.