Lead acid batteries are rechargeable batteries consisting of lead plates with a sulfuric acid/water electrolyte solution. Car batteries and deep cycle batteries use lead acid technology.

All batteries have positive and negative terminals, marked (+) and (-) respectively, and two corresponding electrodes. The electrodes must not touch each other, and are separated by the electrolyte, which facilitates the flow of electric charge between the electrodes. Finally, a collector conducts the charge to the battery's exterior and through the load.

When a battery is inserted into an electrical device, the device completes the circuit between the two terminals and triggers electrochemical reactions within the battery. The anode undergoes an oxidation reaction with the electrolyte, releasing electrons, while the cathode undergoes a reduction reaction and absorbs the free electrons. The product of these two reactions is electricity, which is channeled out of the battery and into the device.

When a secondary battery is recharged, its electrodes undergo an opposite process to the discharging action described above. As the battery charger passes electricity through the battery, one electrode is oxidized and produces electrons which are then absorbed by other electrode. When the battery is fully charged, it can be connected to a load and discharged again.

Technology

The Engineering360 SpecSearch database contains information about several types of lead acid battery construction.

Flooded (or wet) cells have lead plates immersed in a liquid electrolyte solution. Most 12 V automobile batteries use flooded cell technology. If not kept upright, flooded cells may leak and are prone to drying out if water is not added at intervals.

Absorbed glass mat (AGM) batteries are a type of sealed lead acid (SLA) batteries and use an absorbent microfiber glass mat as a separator between plates. Because the mat serves to immobilize the electrolyte, AGM batteries vent less gas than flooded cells and do not need periodically-added water.

Gel cells are another type of SLA battery. In these batteries, fumed silica is added to the liquid electrolyte, causing it to harden into a gel. Unlike flooded cell batteries, they do not need to be kept upright and feature greater temperature resistance.

Specifications

Voltage

Battery voltage refers to the electric potential difference between the positive and negative terminal. Manufacturers typically specify the battery's nominal voltage, although its actual discharge voltage can vary depending on the battery's charge and current. For example, a battery cell with a nominal voltage of 2 V actually discharges between 1.7 and 2.0 volts at a given time. Most round consumer batteries carry a nominal voltage of 1.5 V, while a car battery is typically 12 volts. Depending on the battery materials and application, voltage can range from a fraction of a volt to several kilovolts.

Capacity

The amount of charge a battery can store is known as its capacity. Charge is typically measured in amp-hours or milliamp-hours (Ah or mAh). Most manufacturers specify capacity as the constant current that a new battery can supply for 20 hours. For example, a battery rated at 200 Ah can supply 10 A over a 20 hour period at room temperature. If the current supply to the same battery is increased, the capacity will then decrease.

Reserve Capacity

Reserve capacity describes a fully-charged battery's ability to maintain a useful voltage under a 25 amp discharge. Batteries with higher reserve capacities can operate for a longer period without recharging. When discussing deep cycle batteries, reserve capacity in minutes is a more realistic representation of battery performance than capacity expressed in amp-hours.

Terminations

A battery's terminations provide an electrical contact between the electrodes and the device or load. Lead acid batteries are manufactured with a variety of termination types.

• Screw terminals consist of a threaded rod and accept an insulated metal nut.
• Spring terminals are flat metal strips or spiral-wound wire.
• Solder terminations require the electrical contacts to be soldered onto a flat metal surface or metal tab.
• Plug-in sockets are plugs that mate with an electrical contact's pins.
• Snap fasteners consist of a stud and a socket.
• Wire/cable terminals connect using single or multi-stranded leads, or a cable assembly.

Termination examples. Left to right: Screw, Spring, Wire/cable.

Applications

Batteries are manufactured for use in numerous applications.

• Consumer batteries are used for general purpose consumer applications, such as cameras, radio-controlled cars, toys, and laptops.
• Energy batteries are manufactured for use in oil, natural gas and solar applications.
• Industrial batteries are deep cycle batteries used in forklifts and other industrial applications.
• Medical batteries are used for life support systems, hearing aids and wheelchairs.
• Military batteries are often manufactured to MIL-SPEC requirements.
• Transportation batteries are designed for use in aircraft, boats, automobiles and electric vehicles.
• Stand-by/UPS batteries are used in uninterruptible power supplies (UPS) for emergency lighting and alarms.

References

BatteryFAQ - Car and Deep Cycle Battery FAQ

Battery University - Lead-based Batteries

Image Credits:

Digi-Key Corporation | Newark/element14 | MonsterMarketplace | MCM Electronics