In Telwin's battery charger world everything rotates around the batteries used to supply power to vehicles. A short description of the main characteristics of the different production technologies of batteries used in the Automotive sector follows.
"WET” batteries are traditional and have free acid (flooded); they are accumulators of the Lead-acid type that mainly have these components (see FIAMM TITANIUM photo):
Wet batteries (flooded) are classed mainly in three macro categories according to the constructive technology of the electrodes (positive and negative plates):
a) GREEN: battery CHARGED
b) DARK GREY: battery DISCHARGED
c) WHITE: Electrolyte level very low (the battery needs to be replaced)
They are cutting edge Pb-acid batteries, and their design is based on the technical development of traditional, maintenance free flooded batteries. These batteries were developed over the last years for application to Micro Hybrid vehicles with Start&Stop systems. The main construction characteristics that make AFB batteries different from traditional flooded batteries are: better electrolyte reserve above the plates, negative plates with grids having special alloys and optimised active material for specific functions, double-layer dividers for increasing charge/discharge cycles in the Start&Stop mode, increased electrode (plate) resistance to corrosion. The main advantages when compared to traditional, maintenance free flooded batteries are: more resistant charge/discharge cycles, higher starting power in particular at low temperatures, longer life cycle (when measured in terms of energy output), no maintenance.
See photo of the FIAMM Ecoforce AFB battery.
VRLA (Valve Regulated Lead-Acid battery) type batteries with AGM (Absorbent Glass Mat) technology are Pb-acid batteries where the positive grid is made of a PbCaSn alloy and the negative grid is made of PbCa; they are the only batteries that are completely maintenance free.
The main characteristic that distinguishes a VRLA AGM battery from a traditional flooded battery is the technology used to recombine the gases. These batteries operate on an “oxygen recombination” cycle.
With a traditional flooded lead battery, during the charge phase the two gases in water, namely hydrogen and oxygen, separate. These two gases exit from the caps on the lid and the level of electrolyte inside the battery consequently reduces.
With VRLA AGM batteries, the acid is contained in a special microporous divider made of glass microfiber (Absorbent Glass Mat) that is impregnated with a controlled quantity of electrolyte during the production phase. During the recharge phase, the oxygen that is released by the positive plate because of water dissociation can migrate towards the negative plate, to which it fixes. It then combines with the hydrogen, which recovers the water that had dissociated.
A closed electrochemical cycle is created in this way, which initially and during normal use does not emit gas externally and/or does not consume water.
If the battery is overcharged and a large quantity of gas develops inside it, the excess is released by a safety valve, positioned inside the cover of each cell, that opens. This valve was designed to open at a pressure of about 0.2 bar in new batteries, but in normal working conditions it is closed because it must stop air from entering the battery (the oxygen would discharge the negative plate). This is why these batteries are called VRLA (Valve Regulated Lead-Acid Batteries) with AGM (Absorbent Glass Mat) technology.
It is clear that opening the cover would damage the valves and as such should never be done.
VRLA AGM batteries are more resistant to extreme temperatures, discharge and charge cycles, vibrations and mechanical shock. They are also completely maintenance free, easier to charge (in particular the dynamic type), and they have greater starting power than traditional flooded batteries.
These batteries are very suitable for use with Micro Hybrid vehicles with Start&Stop + B.E.R. systems and this why they have become more widely used over these last years.
See photo of the FIAMM Ecoforce AGM battery.
GEL batteries are made using one of the production technologies used to make VRLA-type batteries. The substantial difference between AGM and GEL batteries is that in the latter the electrolyte is not a liquid but is contained in a special silica gel in which the plate group is immersed, while with AGM batteries the electrolyte is completely absorbed by the special glass microfiber divider.
GEL batteries are not normally used for starting applications in the automotive sector because high working temperatures inside the vehicle motor area significantly increase the volume of the gel, which causes repercussions on electrical performance and battery life. On the other hand, very low temperatures cause the GEL to concentrate inside the cell, which increases the internal resistance of the battery; this has a negative effect on the cold start current (-18°C), which becomes much lower than that of AGM or flooded batteries.
GEL batteries are therefore more suitable for energy applications than for power applications, and they are used in industrial applications where high resistance to discharge and charge cycles and/or greater buffer mode life are required. They are also used for powering on-board services in the nautical and free time (Motorhomes) sectors as an alternative to AGM batteries.
Thanks to FIAMM SpA for the pictures and the support provided solely to implement the part relative to the type of batteries. Trademarks and images belong to FIAMM SpA; any transfer of the same to a third party is forbidden; the brand and the images cannot be used for any other purpose except made for the present document.