Determine potential energy for a 6 volt battery that has 3000C of charge Q stored.

The potential energy for a 6 volt battery that has a stored charge in it of 3000 Coulombs would be 18,000 Joules.  Potential energy is the ability to do work and represents the capacity the battery has to achieve a certain level of work.  The formula for calculating potential energy for a battery may be represented like this:

Electrical Potential (Volts)  =  Work or Potential Energy/Charge (Coulombs)

In this question, we have the electrical potential already, 6 Volts.  We also have the stored charge, 3000 Coulombs.  We can calculate the missing potential energy amount by multiplying both sides by the 3000 Coulombs:

(6 Volts)(3000 Coulombs)  =  (PE)(3000 Coulombs)/3000 Coulombs

18,000 Joules  =  PE, potential energy

Remember that one Volt is equal to one Joule/Coulomb, so when you multiply the left side by 3000 Coulombs, the Coulomb units will cancel out, leaving Joules as the correct energy unit designation.