About Batteries

What is a battery?


A battery is an electrochemical device that stores and delivers energy. Energy is chemically stored in the battery and when the terminals of the battery are connected through a resistive load, electrical energy passes through the circuit.


Lead-acid Batteries


Automotive lead-acid batteries are commonly referred to as starting batteries, which are generally 12 volts (12V) and are rechargeable. These batteries supply power to the starter and ignition system to start the engine and to power additional auxiliary items such as clocks, computers, navigation systems and any other device that requires constant power.


Lead-acid batteries also supply extra power needed when the vehicle’s electrical load exceeds the supply from the charging system (alternator) and acts as a voltage stabilizer in the electrical system, evening out voltage spikes and preventing them from damaging other components in the electrical system.


Anatomy of a Lead-acid Battery


A 12V lead-acid battery contains six separate cells at two volts each and a 6 volt with 3 separate cells at two volts each. The cells are connected in series by connections through the cell partitions. Each cell contains an element that consists of positive and negative plates. The battery is then filled with liquid electrolyte (a solution of sulfuric acid and water) or as it is commonly called, battery acid.


Batteries are made of five basic components:


  • Positive plates
  • Negative plates
  • Separators – usually a micro-porous polyethylene synthetic material
  • Polypropylene container
  • Liquid electrolyte


Plates are comprised of two parts – the grid and the paste, both made of lead. The paste is soft and is the active material that chemically stores the energy. The grid provides a skeletal framework for paste adherence. Grids are made of lead alloys that resist corrosion and conduct electricity to and from the plate.


Positive and negative plates are stacked in an alternating fashion, with separators between the plates to prevent electrical shorting and to enable battery acid to flow back and forth. Both the positive and negative plates are connected at the top by a cast-on-strap that is welded to the plates. When a battery goes from a charged state to a discharged state, it is called battery cycling. During discharge, energy is released from the battery as is demanded by the electrical system. The battery is recharged with energy generated by the alternator.


Group Size


Battery Council Industry (BCI) specifies standard battery sizes and configurations by group size. This includes standard overall size – length, width and height of the battery – and standard terminal type and position.


Cold Cranking Amps (CCA)


This industry rating measures the power a battery has available to start a vehicle’s engine at -17.8 degress celcius or zero degrees Fahrenheit.


For a 12V SLI (Starting, lighting, ignition) battery, BCI defines CCA as the amount of current (number of amperes) a lead-acid battery at -17.8 degrees Celsius or 0 degrees Fahrenheit can deliver for 30 seconds while maintaining at least 7.2 volts.


Reserve Capacity (RC)


A battery’s RC represents the length of time a battery can maintain a vehicle’s electrical needs in the event of a charging system failure (alternator failure). BCI defines RC for a 12V SLI battery as the amount of time (in minutes) that a battery can deliver 25 amps at 27 degrees Celsius or 80 degrees Fahrenheit  while maintaining terminal voltage of at least 10.5 volts.


Battery Types

What are the major types of lead acid batteries?

Batteries can easily be divided in two ways, by application and construction. The major applications are starting, dual purpose, and deep-cycle. The major construction types are flooded (wet), gelled, and AGM (Absorbed Glass Mat).


Sealed Maintenance Free Battery


Sealed batteries are commonly known as maintenance free batteries. They are made with vents that (usually) cannot be removed. A standard auto or marine maintenance free battery is sealed, but not fully leak proof. Sealed batteries are not totally sealed since all batteries must allow gas to vent during charging. There are sealed lead acid (SLA) batteries that are non-spill able.


AGM or Absorbed Glass Mat Battery


The newest type of sealed non-spill able maintenance free valve regulated battery uses "Absorbed Glass Mats", or AGM separators between the plates. Because of the way they are constructed, an AGM Battery will not leak acid if broken.


What are the advantages of the AGM battery?


The primary advantages an AGM Battery has over a conventional battery are: zero maintenance, vibration resistance, quicker charge recovery, no outgassing of fumes, non-spilling (even if they are broken), and can survive most freezes.


AGM batteries are "recombinant" – which means the Oxygen and Hydrogen recombine inside the battery.


These use the gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.


AGM batteries have a very low self-discharge rate (from 1% to 3% per month). So they can sit in storage for much longer periods without charging.


The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.


What is a Gel Cell Battery?


A gel battery design is typically a modification of the standard lead acid automotive or marine battery. Silica gelis added to the electrolyte to reduce movement inside the battery case. Many gel batteries also use one way valves in place of open vents, this helps the normal internal gasses to recombine back into water in the battery, reducing gassing. "Gel Cell" batteries are non-spill able. Gel cells must be charged at a lower voltage (C/20) than flooded or AGM to prevent excess gas from damaging the cells. Fast charging them on a conventional automotive charger may permanently damage a Gel Battery.


Construction Types


Wet Maintenance Free


Magnacharge Wet Maintenance free batteries are designed with Lead and Calcium alloy in the positive and negative plate chemistry or formulation.


A more functional and effective design than traditional batteries with removable vent caps.  Sealed batteries of this design have longer water retention and are a far more robust battery for to days climates and conditions.


Other benefits are:


Less preventive maintenance due to less water loss


More forgiving when accidentally overcharged


Reduced terminal corrosion and ventilation


Smaller self-discharge rate


Less risk to consumers because there is less to service


Wet Marine/Recreational Vehicle (RV)


Wet marine/RV batteries are available in three different versions--starting, dual purpose, and deep cycle.


The starting marine/RV battery is designed similar to that of a wet car/starting battery with carrying handles and is designed for high current and shallow discharges. The wet dual purpose marine/RV battery is a compromise between a starting and deep cycle battery that is specifically designed for high vibration in marine/RV applications.


The deep cycle marine/RV battery is designed for deep discharge applications such as a trolling motor, golf cart, AWP and floor care equipment.


A marine/RV deep cycle or dual purpose battery will work as a starting battery if it can produce enough current to start the engine.


Good ventilation is required for all wet (or "flooded") batteries to dissipate the gasses produced during charging. For saltwater applications use only a sealed AGM or Gel Cell battery to prevent the formation of deadly chlorine gas that can occur if battery electrolyte is mixed with saltwater.


AGM (Absorbed Glass Mat)


Sealed Absorbed Glass Mat has a glass mat between the plates. They have all of the advantages of the "Maintenance Free” batteries plus:


Much safer then wet batteries (due the hydrogen gas recombination during charging)


Do not require water.


Lower self-discharge rate (typically 1%-2% per month)


In the perfect conditions AGM batteries can offer Longer service life


Better vibration endurance


Can be used in saltwater applications


Spill proof and can be mounted in virtually any position (because they are sealed)


Can be used inside a semi-enclosed area, like the passenger compartment or trunk


No sulfation from electrolyte stratification or water loss


Battery Terminology:


  •  Voltage/Electromotive Force ( Volt,V,E ): The electrical pressure driving electrons through a conductor.
  • Open Circuit Voltage (OCV): The voltage of a battery in the absence of a charge or discharge current.
  • Voltage Under Load (VUL): The voltage of a battery in the presence of a discharge current.
  • End of Discharge Voltage (EODV): The voltage of a battery at the end of discharge while under load.
  • End of Charge Voltage (EOCV): The voltage of a battery at the end of charge while still on charge.
  • Specific Gravity (SG): The density (mass/volume) of the liquid (electrolyte) relative to water, at the same temperature.  The density of water is 1.

             Example: 1.280 kg/l = 1.280

                                       1.000 kg/l

  •  1.280 is referred to as “twelve-eighty” acid.
  • The difference between 1.280 and 1.275 is referred to as “5 points”
  • Open Circuit Voltage/Cell » Specific Gravity/Cell + 0.845
  • Open Circuit Voltage and Specific Gravity µ State of Charge (SOC)
  • Ampere (A): The rate of flow of electrons.Electrical current.
  • Ampere-Hour (AH): A measure of current over time. Battery capacity (Ampere-Hour = Amps x Hours).
  • Watts (W): The rate of using energy to do work. Power (Watts = Volts x Amps).
  • Watt-Hour (WH): The measure of power over time. Energy (Watt-hours = Volts x Amps x Hours).




  • Batteries need to be overcharged to ensure proper mixing of the electrolyte and avoid stratification.
  • Batteries should be charged after every use to ensure they are never stored in a discharged condition.
  • If batteries are stored for extended periods of time they should be charged approximately every 6 weeks.
  • Lead-acid batteries DO NOT have a memory affect (they do not need to be fully discharged prior to charging)




  •  Always wear protective clothing, gloves and goggles when handling batteries.
  • Do not smoke near batteries.
  • Neutralize acid spills with baking soda immediately.
  • Charge with vent caps securely in place.
  • Provide proper ventilation during charging to prevent gas build up.
  • Keep flames, sparks or metal objects away from batteries (use insulated tools).
  • Keep batteries clean and dry.
  • Check that all vent caps are tight.
  • Check that all connections are tight (see recommended torque values).
  • Use a solution of baking soda and water to clean if there is acid residue on batteries or corrosion on the terminals.




  • Terminal protectors or protectant spray can be applied to terminals to reduce corrosion.
  • Batteries should be fully charged prior to and during storage.
  • Never store discharged batteries.
  • Store batteries in a cool, dry place to minimize self-discharge.
  • Recharge batteries prior to putting them back into service to ensure they are fully charged




  • Add water to cells (distilled water is recommended).
  • Never add acid to cells this is dangerous and will alter the chemistry.
  • Add water after fully charging batteries to a level of 1/8” below the bottom of the fill well or to maximum level indicator.
  • Do not overfill the batteries this will dilute the electrolyte
  • If the plates are exposed in discharged batteries, add water to a level just above the plates.
  • Never add water to discharged batteries if the electrolyte is visible above the plates.