Activity 1.14 - How much energy supplies a battery?

• Understanding that battery stores energy that is consumed by load
• Understanding how much charge and energy is supplied by a battery measuring current and voltage in a circuit.
• Understanding the properties of good battery in terms of life and economy
• Understanding what parameters producers take into account in order to build a battery appropriate for its application.

Batteries of the same size (e.g., AAA, AA, C, D) and different producers, connecting leads, computer, interface and software (e.g. CMA Coach6), voltage sensor (not necessarily), current sensor (if current sensor is not available, the resistor of known value RA is recommended, e.g. RA=1ohm-cm in order to measure current)

The activity is aimed at understanding the battery properties in terms of energy it can supply to the circuit and what battery is considered to be good. During one lesson students set several measuring spots depending on how many batteries are going to be measured. They can use the same emf value batteries from different producers (non chargeable and chargeable, eventually). With the help of computer and sensors they measure current and voltage across the external load during battery discharging. Since the measurement can last up to 24 hours, it is recommended to start the measurement during one lesson and the next day to save the results. Then, students working in groups of 2-3 analyze the results. Each group analyzes one of the measured batteries. Firstly, they determine battery capacity from the area under current-time graph. Then they analyze the power delivered to the external part of the circuit and hence they count the energy amount delivered to the circuit by determining the area under power vs. time graph. Finally, the groups compare their results for batteries of different producers in term of energy delivered to the load and they draw conclusions. 

Measurement is done in a guided inquiry mode according to the instructions in the worksheet. Considering the students level of understanding, teacher can decide about the bounded inquiry mode. This activity offers a lot of industrial applications. They include the knowledge about other properties of the battery that are important for the consumer (chargeable, non-chargeable, voltage, current, energy supply, life, economy, price, weight, self-discharging of batteries, memory effects of chargeable batteries). The activity can be followed by an open inquiry assignment aimed at formulating some other research questions considering the properties of batteries, e.g. the self discharge, the effect of temperature on the battery performance, the memory effect, battery performance when the operation is interrupted several times (the effect on the terminal voltage and current), etc. Students design an experiment in order to answer the research question.

• What energy is stored in a battery?
• How much charge is stored in a battery?
• What is the energy delivered into the circuit during the battery discharging?
• What parameters should be taken into account when you buy a battery for a certain purpose? Research questions can include:
  • What do we mean by self discharge, memory effect?
  • What is the influence of temperature on the battery performance?
  • How does the battery work when its operation is interrupted several times?