Looking Inside a Lead Acid Battery | Home, DIY & Stuff

Looking Inside a Lead Acid Battery

November 21, 2014

lead acid car battery cut awayHere’s something just for interest’s sakes.  Photos of a modern, but humble lead acid car battery and its internal electrode plate arrangements for those who may not have seen similar before.

Common lead acid batteries in cars and trucks work by developing and storing electric potential between sets of positive and negative electrode plates.  The electrodes are commonly made of Lead (Pb) and Lead Dioxide (PbO2) mesh and paste, separated by a non-conductive porous material to stop them touching and short circuiting.  The battery cells are submerged in approximately 35% Sulphuric Acid (H2SO4(aq)) which acts as an electrolyte and allows electrons to flow between the plates and to deliver current when the battery terminals are connected to a circuit.

The basic energy storage and delivery concept of lead acid batteries was invented over a century and a half ago by French physicist Gaston Planté.  Since that time, this kind of battery chemistry has been developed to become a standard and efficient workhorse in everyday life for us all.

lead acid car battery cut awayDifferent types and designs of lead acid batteries are available for differing applications, but the basic charge chemistry and concept at their core remains similar.

The battery shown is a shallow cycle lead acid battery (also named flooded, starter or SLI battery) as commonly used in cars and trucks.  It is designed to deliver the short, powerful bursts of high amperes of electricity required to start engines, drive ignition of spark plugs and illuminate car lights, etc.  It does not generally lose a large amount of charge at any one time under normal conditions before being recharged by the vehicle’s alternator.

For a typical car battery, the pairs of plates (elements) are placed in 6 separate separate cells in the battery box.  This produces a total of 12.6V with each element providing a potential of approximately 2.1V when the battery is fully charged.  One open cell is shown in the photographs.

There is no doubt.  Despite the basic concept of these batteries remaining the same over the decades, the quality, design and construction of batteries has changed dramatically.

lead acid car battery cut awayLong ago, I remember dodging splatters of Sulfuric Acid while draining electrolyte from car and truck batteries.  That was just before smashing the thick plastic walls of the bulky battery boxes, and melting the crudely designed lead plates inside into DIY fishing sinkers.  (All while staying upwind to avoid the lead dioxide fumes!  Something that in hindsight, was potentially quite dangerous and certainly not advisable for health reasons!)

These days, the plastic boxes of a lead acid batteries are far more lightweight and compact, yet still very strong. The electrode plates inside, rather than being crudely cut plates, are formed of mesh containing a smoothed on paste of Lead or Lead Dioxide to form either the positive or negative electrode.  The plates are separated and insulated by a stiff and neatly folded non-conducting permeable layer.

Other lead acid battery types that are available are variations on this basic lead acid battery design. 

Deep cycling lead acid batteries have thicker plates and are used in applications where the charge is gradually and repetitively drawn down by a (relatively) large amount over time, before being re-charged again.  An action that usually quickly destroys normal car batteries.  Due to their characteristics, deep cycle type batteries are commonly found in solar and other renewable energy storage applications.   Sealed, or “maintenance free” (ie: maintenance impossible) lead acid batteries have further variations on the theme and are used in lawnmowers, motorbikes, etc.  Other specialty and industrial lead acid battery types are also important in domestic and commercial applications.

lead acid car battery cut away

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