Mar 02 2010

Batteries: Why So Many Sizes?

AA, AAA, C, and D!  No, batteries…not bras.  Have you ever wondered why there are so many sizes of standard batteries?  Have you ever looked closely, seen that they all produce 1.5 volts, and wondered why there are so many sizes of standard batteries that do the same thing??  Here’s why.

It begins with the old physics formula (I’ll keep it simple, I promise!) for the relationship between Current, Voltage, and Resistance:

I = V / R


I = Current (amps) *the “flow” or (I)intensity of electricity
V = Voltage (volts) *electrical potential or “oomph”
R = Resistance (ohms) *opposition to steady flow of current, often dissipated in heat

Now, we know that AAA, AA, C, and D batteries all say they produce 1.5 volts.  We also know that they grow in physical size (from AAA up to D).  This allows them to store more progressively more zinc, manganese dioxide, and potassium hydroxide – the pasty chemicals that store the battery’s energy.  With more surface area inside the battery, the resistance to the electrical current is lowered (don’t ask why).  When resistance (R) is lowered, the voltage (V – which we know stays the same) is divided by a smaller number, which makes the current (I) come out larger.  This is represented by:

I = V / R

So as the battery grows larger in cell size, the output current increases.  For this reason, high-powered (drawing a high current “flow”) flashlights, stereos, and boomboxes (!) require D-cell alkaline batteries while remotes and smaller gadgets require only AA or AAA.  Cameras tend to burn through batteries quickly because they are sized for AA but draw a high current flow, draining the battery in a flash (pun intended).

While we’re on the topic, and since I mentioned the potassium hydroxide inside the battery, know that this is the source of the dreaded leakage that crusts over your appliances and flakes to high hell-o.  This substance is caustic and can irritate skin, eyes, and respiratory systems as well as corrode copper, varnish, and wood.  Check your alkaline batteries often to prevent damage to your electronics or furniture.

Do you still use 9-volts?  Do you still have a boombox?  What random questions do you want answered?  Comment and share!

Photo credits:  Batteries courtesy varun2911
LeakedBattery courtesy Turelio


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