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Thread: Batteries

  1. #1
    Senior Member Jim_S-V6_2004's Avatar
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    Batteries Info

    Information on car batteries


    A "battery" is a collection of electrical cells which produce or store electric charge.

    All batteries for combustion-engined cars are composed of 6 lead and acid ("lead/acid") cells, each of which produces 2.1 volts.

    The battery produces or stores a total of 12.6 volts when fully charged.

    Each cell is made of a set of positive electrodes (known as "plates") and a set of negative electrodes (plates) which are both immersed in an electrolyte mix of sulphuric acid and distilled water, which works by chemical reaction between the positive and negative plates and the acid electrolyte.

    Battery History

    The original experimental cells were called "accumulators" since they stored electricity. After many variations, their electrodes were made of lead and lead oxide.

    Since pure lead is very soft and easily distorts, the original car battery plates were made from a lead & antimony alloy to harden them.

    These lead/antimony batteries became the standard construction for car batteries through the entire 20th century.

    As car technologies came to demand more and more electricity, more battery capacity has been needed but this resulted in larger and heavier batteries, so better battery technologies are needed in order to keep the battery physical size and weight within acceptable limits.

    There is ongoing research to develop new battery technologies for electric and hybrid vehicles.

    Calcium Batteries

    Batteries in which the electrolyte is in liquid form, including lead/antimony and lead/calcium batteries, are known as "wet cell" or "Flooded" or "Enhanced Flooded" batteries.

    They are also known by their application, "Starting, Lighting and Ignition" (SLI) batteries.

    Some years ago a lead & calcium alloy was developed for battery plates which improved capacity and efficiency, and reduced the battery size, so these "calcium" batteries have become today's standard for car batteries, and lead/antimony batteries were discontinued.

    Calcium batteries can have either only one plate made of calcium alloy, which are known simply as "calcium" batteries, or both plates made of calcium alloy, which are known as "calcium/calcium" batteries.

    Some batteries have additional ingredients such as calcium, silver, tin and others in the alloy.

    The presence of calcium is not always made clear by manufacturers in their data.

    Note that most Flooded batteries, including calcium batteries, are not entirely sealed but have a side vent which should be connected to a breather hose leading down outside the car to vent any electrolyte overflow.

    Some still have removable cell covers to allow inspection and top-up with distilled water if needed.

    AGM Batteries

    AGM ("Absorbent Glass Matting") batteries, in which the acid electrolyte is absorbed in fibreglass matting which is pressed to the negative and positive plates in various ways, are available in both rectangular versions resembling flooded batteries, and cylindrical cell versions, known as "spiral" versions, like the Optima series in which the plates are made of pure lead and rolled up.

    AGM batteries are more efficient and last longer in "deep discharge" applications than flooded batteries. They are sealed, and completely maintenance free. They do have a vent valve which releases any excess pressure but this is purely for safety.

    "Stop/Start" batteries can be either Flooded wet cell, or AGM batteries. Those usually have more plates than their normal versions. AGM batteries are better suited to Stop/Start applications.

    Gel Batteries

    Gel batteries are made for applications where they are shaken or inverted, and are not normally intended for use in cars.

    In Gel batteries, the acid electrolyte is in solidified (jellified) form, not liquid.

    State of Charge

    The State of Charge of a battery is its current charge as a percentage of its potential full charge capacity.

    The battery's State of Charge at any time is proportional to its voltage at the time of measurement.

    The State of Charge of calcium and AGM batteries are different.

    Calcium batteries are fully charged and at full capacity at 12.7 volts after removing any surface charge after charging, by allowing the battery to rest for 6 to 8 hours or by turning on the headlamps for 3 minutes.

    An AGM battery is fully charged and at full capacity at 12.85 volts after removing any surface charge after charging, as described above.

    The charts below illustrate the State of Charge of these batteries.

    Calcium (Flooded/wet cell) Battery State of Charge

    AGM Battery State of Charge


    How batteries work

    AGM Battery Construction

    OPTIMA AGM Batteries

    Battery State of Charge (Flooded)

    Charging and Testing

    Last edited by Jim_S-V6_2004; 07-01-19 at 23:07.

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  3. #2
    Senior Member Jim_S-V6_2004's Avatar
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    I thought it might be appropriate to update battery info since battery technology is improving due to stricter emissions regulations.

    Remember that "Flooded Lead Acid" does Not mean old lead/antimony alloy plated batteries, it means any wet cell battery with liquid acid/distilled water electrolyte.

    And all car batteries are "lead/acid". They all need and contain lead plates and acid electrolyte. They have positive and negative plates (anodes and cathodes) in each cell, which are made of some form of lead alloy.

    All modern batteries since about 2004/5 have calcium/lead alloy plates in them, some have calcium/silver/lead or other specialised alloy plates.

    And wet cell batteries are still vented. There is sometimes a vent hole on the left or right side or both, for a hose to be fitted to drop any evaporation or spillage of the electrolyte out and below the car so it does not corrode car parts around it. New batteries have small plastic plugs in the vent holes, one of which should be removed and the vent hose fitted.

    Some wet cell batteries are completely sealed but have one or more pressure release valves for extreme conditions. Those are known as Valve Regulated Lead/Acid ("VRLA") batteries.

    "Calcium/calcium" labelling on a battery means that both plates in each of its 6 cells are made of lead/calcium alloy.

    AGM batteries have their electrolyte absorbed in fibreglass matting so it's not exactly liquid nor gel, but is not free to slop about or escape either.

    There are also AGM batteries which have cylindrical "spiral" cells and are obvious by their shape of a pack of 6 cylinders in a plastic container:

    "Gel" batteries contain acid electrolyte in jellified form which cannot slop or spill, so they are often completely sealed. They also known as "dry" batteries, and are suitable for sports, off-road use and boats.


    Old lead/antimony car batteries needed 13.6 volts to fully charge. Calcium alloy plated batteries require 14.4 volts to fully charge. AGM batteries usually require 14.8 volts.

    However, new wet cell technology car batteries containing plates of "pure lead" are becoming available, which should require lower charging voltages of 13.6 volts, conforming with new emissions regulations requirements.

    Most smart chargers will not charge a battery which has drained below 10.5 volts. There are ways to trick them into charging.


  4. #3
    Senior Member Jim_S-V6_2004's Avatar
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    For chargers and charging, see


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