Lead Acid Battery

A battery with electrodes of lead oxide and metallic lead that are separated by an electrolyte of sulphuric acid.

The overall reaction is:

PbO2 + Pb + 2H2SO4 <=> 2PbSO4 + 2H2O

Some batteries manufactured for use in very hot or very cold climates may have stronger or weaker acid. If so, it is usually marked on the battery.

Most Lead-Acid batteries will have a specific gravity in the range of 1.1 to 1.3, with most fully charged batteries being about 1.23 to 1.30 (Note: some hydrometers multiply this number by 1000, so 1.3 would read as 1300.)

A very old lead acid battery showing the arrangement of plates in each cell.

The advantages of the lead acid battery are:

The disadvantages are:

Absorbent Glass Mat

A separator technology used in some sealed lead-acid batteries in which the glass-mat separator absorbs 100% of the electrolyte. Because of the immobilized electrolyte, an AGM battery will not leak or spill and does not require water addition.

Automotive Terminal Post

A round post made of lead used on engine starter batteries.

Deep Cycle

A lead acid battery designed to operate over deeper discharges, the normal design change is to use thicker lead plates.

Float Voltage

The voltage at which the battery is floated, or just enough current is supplied to equal the self-discharge of the battery.

For lead acid batteries this is typically about 14.2 volts for a 12 volt battery.

Flooded Cell

A design for lead-acid batteries where the electrolyte is an ordinary liquid solution of acid.

Gel Cell

A technique for sealed lead-acid batteries. The electrolyte solution is in a gel form, usually silica gel, instead of plain liquid.


A style of battery terminal, shaped like an L, with a flat vertical part to which the cable is bolted.


The metal plates, usually lead or lead compound, immersed in the electrolyte in a battery.


A condition in which the concentration of acid is greater at the bottom of the battery than at the top. Normally caused by continued undercharging.


The accumulation of lead sulfates on the plates of a lead-acid battery. When enough plate area has sulfated, the battery will not be able to provide enough current and will normally need to be replaced.

Universal Terminal Post

A style of battery terminal, with a round post similar to the automotive post, but with a threaded stud in the center of the post.

Valve Regulated Lead Acid Battery (VRLA)

A lead acid battery that uses pressure valves that open only under extreme conditions. VRLA batteries are sometimes called recombinant batteries.

Vented Battery

A battery in which the gaseous products of electrolysis and evaporation are allowed to escape into the atmosphere as they are generated. These batteries are commonly referred to as Flooded Batteries.

See also: Absorbed Glass Mat Battery, Absorbent Glass Mat Battery, Battery, Battery Acid, Bipolar Lead Acid Battery, Peukert Equation, Sealed Battery, Spiral Wound Lead Acid Battery.

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Subjects: Electrochemistry Electronics