How it Works

How the Battery Pack Voltage Works

A single AAA alkaline battery is considered to be a 1.5 V supply when used in rough calculations.  Two alkaline batteries connected in series (end-to-end) have their voltages added.  Since the AAA battery holder connects the two AAA batteries in series for you, it is considered to be a 3 V supply.  

When alkaline batteries are new, they typically measure around 1.6 V.  As they supply current to circuits, devices, or motors, they lose their charge.  Charge is the accumulation of electrons, and a battery’s charge decays as it supplies current (the flow of electrons).  By the time the alkaline batteries in series reach 2.8 V, the batteries are considered “dead” for micro:bit servo control.  

Although alkaline batteries have a voltage charge relationship where voltage decays with charge, there are also different kinds of batteries that have different voltage to charge relationships.  For example, lead-acid batteries found in older model cars have to be tested by a machine that applies a load and measures how much current the battery supplies.  Another example, nickel-metal hydride (NiMH) rechargeable batteries have a much smaller change in voltage to indicate their charge level.

 
Try This: Measure Tired Batteries

If you have some dead AAA batteries:

• Open the battery pack’s plastic cover and replace the new batteries with the dead ones.
• Plug the battery pack back in.
• Measure the bus strip’s (+) and (-) rails, and make a note of it.  The voltage will probably be below 2.8 V.
• Make sure to put the fresh AAA batteries back in the holder when you are done, if you are going to keep working.
• Also, make sure to remove the batteries from the pack when not in use.