Innovative Lives

Experiments with Solar Shingles

The Story of Inventor Subhendu Guha


How long will a battery hold its charge?

Battery Multimeter
Headlight Test Leads


  • 1 12-Volt sealed rechargeable battery
  • multimeter
  • test leads
  • 12 Volt DC auto headlight

How to take measurements:

  1. To measure voltage, turn the knob on the multimeter to 25 DCV, which means the multimeter can measure 0 to 25 DC volts. Touch test probes to the circuit. (This means touch the test probes to the wires of what you are measuring, like the shingle wires or the battery terminals). One probe should touch each wire or terminal. Read and record the voltage.
  2. To measure the resistance on the circuit, turn the knob on the multimeter to RX1 Ohms. Touch the test probes to the circuit. Read and record the resistance.
  3. Calculate current with Ohm's law.

How long will a battery hold its charge?

  1. First check to see if the battery needs to be charged by measuring the voltage. If a 12 volt battery is fully charged, the multimeter should read 12 volts. If your battery is charged, you're ready to start!
  2. Connect the battery to the auto headlight.
    Do not touch the bulb, hold the light by its base.Bottom view of headlight
  3. Once every hour, disconnect the battery, measure voltage and resistance, and calculate current. Continue making measurements until the battery loses its charge.
How long did the battery stay charged?

How did you know when the battery had lost its charge?

How could you make the battery last longer?

This activity was created by Emily Wilson, Lemelson Center

All text and images © Smithsonian Institution. Updated 26 February 1999.

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