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.