In the last article we knew about basics related to a lead acid battery. With this post we will try to explore more about the automobile batteries. The main focus would be on introducing you to some basic terminologies related to batteries and telling you some very interesting facts about which you are unaware.

An automobile battery being refilling with electrolyte
Adding distilled water to battery
Voltage

If you measure the voltage between the two terminals of a 12 volt fully charged lead acid battery , you will find it to be 13.2v instead of 12v. Have you ever tried to find out the reason behind it. Let me tell you, this all happens because the 12 lead acid battery is made of 6 small cells of 2.2 volts. When the battery is fully charged the cell voltage becomes 2.2 volts and hence the total voltage of 6 cells comes out to be 6×2.2 volts i.e. 13.2 volts. If you leave a fully charged battery for some times the voltage of the cells settle at 2.1 volts, and hence the total voltage of the battery comes out to be 6×2.1 volts i.e 12.6 volts. So in reality the voltage regulator of a 12 volt battery is not exactly 12, you may find different voltage values depending on the charging conditions.

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Ampere-hour

The amp-hour is the measure of the capacity of a battery . It represents the amount of power a battery can store. The amp-hr of battery difines an average amount of current the battery can supply for a fixed amount of time. Generally the average is calculated for a period of 10 hours i.e a battery having rating of 2.5 amp-hour can supply 0.25 ampere of current for 10 hours. The current supplied by battery is not constant. It  varies depending upon the  the load. A low resistance load can draw a higher current while a higher resistance load will draw a lower current.  The same battery having 2.5 ampere-hour capacity can also supply 2.5 ampere of current for a period of 1 hour. 

Difference between an inverter battery and an automobile battery
This is probably the one thing about which you might have never thought about. Most of the people think that both these batteries are same, but that’s a misconception  These two are completely different in terms of performance as well as construction. The basic difference lies in the purpose for which they are used. The    inverter batteries are designed to supply current over a long period of time. On other hands the automobile batteries are designed to operate starter motors, which require very large amount of current. So the main objective of an automobile battery is to supply very large amount of current for a short duration of time. These batteries are designed, keeping their basic functions in the mind. The automobile batteriess have large number of thin plates so as to provide large surface area for reaction and hence to produce very large amount of current. But, since the plates of these batteries are thinner, they can not be discharged to very low voltage. Doing this will damage the plates and will make the batteries useless.
The inverter batteries have thicker plates and also the number of plates is significantly lower as compared to the automobile batteries. That’s why they can be discharged to very low voltages . The amount of electrolyte is greater in inverter batteries as compared to the automobile batteries. This helps in carrying out the discharging reaction for a longer period of time and hence these batteries are able to supply the current for a longer  time. These batteries are also called deep cycle batteries since they can be discharged to very low voltages.
Types of automobile batteries

The batteries used in automobiles are generally of two types.
1) Flooded batteries
2) Maintenance free batteries.
 Let’s discuss both these types one by one.

Flooded batteries
Motorcycle battery flooded type
A flooded type battery
These batteries are not in vogue now days. They are being replaced by maintenance free batteries. These batteries contain liquid electrolyte and the whole battery chamber is flooded with the electrolyte. They had arrangement to refill the electrolyte. If we charge the lead acid batteries using higher amount of current the water in electrolyte may be hydrolysed to produce Hydrogen gas.  Also a higher temperature is produced during charging and discharging  which causes the electrolyte to evaporate. The accumulation of large amount of Hydrogen and water vapour inside the battery may lead to explosion. To avoid this a vent is provided in the battery. This vent helps in discharging these gases to the outside environment. This discharging of gases lowers the level of electrolyte in battery which needs to be replenished to maintain the original level.

Sealed or maintenance free batteries

Valve regulated lead acid battery or maintenance free battery
A VRLA battery

These batteries are sealed and do not need the refilling of electrolyte. These batteries contain pressure regulated valves which opens when the pressure of gasses inside the battery reaches  a particular level. These valve stops the Hydrogen and water vapour produced inside battery. The water vapour condenses and mixes again with electrolyte while the Hydrogen once again get involved in electrode-electrolyte reactions.  But all these happens only till the pressure of gases remain within the safe limits. These batteries are safer and do not cause spillage of electrolyte. They can also be used in any orientation which makes them suitable to use in automobiles.



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