Resistor--capacitor (RC) circuit labs help students, but most courses don't include them because of complications and cost. This work presents an easy and inexpensive Arduino-based lab on the charge and energy transfer between two capacitors with different values of the initial electric charge when they are connected through a resistor. Capacitors are electromagnetic devices widely described in calculus-based introductory physics courses. The concept of capacitance, the determination of the capacitance in planar and cylindrical geometries, the description of the series and parallel combinations of capacitors, or the evaluation of the electric energy stored in them are classic topics studied under electrostatic equilibrium conditions. Charge and discharge of a capacitor through a resistor is also studied in order to experimentally determine the capacitance of the capacitor or measure the electric charge stored in it. Energy balances in the charging and discharging processes of a capacitor are also widely discussed in textbooks. To get a better understanding of the basic concepts, other complex exercises are included in these courses. Among them, one can find the determination of the final charge and energy stored in each of the two capacitors, with different initial charge states, which are combined in parallel. In addition, the study of the charge through a resistor of a discharged capacitor by using a charged capacitor is also a classical exercise when one studies in depth the RC circuit. However, lab exercises covering these last topics are lacking in introductory physics courses. This is mainly due to the need to use complex experimental setups to simultaneously handle various power sources and various multimeters.