A car battery has an electrolyte that is made up of water and acid. There are electrodes and cells which are suspended in the electrolyte.
In most cases, the electrolyte is diluted in the ratio of 65% water and 35% acid however this ratio may change depending on what the battery is used for. To measure the concentration levels of sulfuric acid a specific gravity test of the acid is done.
Specific gravity simply means the ratio between the densities of two liquids that are mixed. In our case, the two liquids are water and sulfuric acid so the specific gravity will give the ratio between the density of water and the density of the sulfuric acid
The specific gravity of the electrolyte in starter batteries like that of a car is recommended to be 1.28-1.30. For the preparation of the battery, the right specific gravity is really important.
The specific gravity of the electrolyte rises when water is lost. When it rises beyond the advisable range, it will lead to corrosion of the battery.
The reverse is true in the sense that when the battery has too much water the specific gravity of the electrolyte falls and this means the electrolyte will have fewer sulfur ions and this has a direct effect on the capacity of the battery to hold a charge.
How Does the Battery Loose Water?
Below are some of the ways through which a battery might lose water.
Through Electrolysis During Charging
During the discharging of a fully charged battery, sulfur is extracted from the battery which reacts with lead and the lead oxide plates to produce lead sulfate. As more sulfur is drawn from the battery the solution is left with more water. Water has a low specific gravity. During charging this process is reversed.
When charging is done, the lead sulfate which was formed during discharge is broken down into lead and lead oxide and sulfate which then combines with water in the electrolyte to have sulfuric acid formed. This causes the specific gravity of the solution to rise.
It is during the charging process that the water also undergoes electrolysis. This is a process through which the water breaks down into its constituents which are hydrogen and oxygen gases.
Much of the gases generated will escape from the batter when dealing with the flooded lead-acid batteries. As these gases escape the water levels will reduce. The gases however are contained in an environment where they cannot easily escape but will recombine back to form water in sealed batteries or valve-regulated lead acid batteries.
Through Evaporation
The electrochemical reactions during charging and discharging produce heat as a by-product therefore the name exothermic. This heat that is produced may cause water in the electrolyte to evaporate and this will lead to reduced water levels in the electrolyte.
To prevent this, the battery should be operating in an environment where the heat produced can be easily dissipated to the environment without the heat having to build up to the extent of causing evaporation.
Battery Leakage
When the casing of the battery is damaged, the battery acid will leak out. The acid may also leak if the battery is not put in an upright position. When leakages occur, the electrolyte levels drop below the desired level.
What Are the Effects of Water Loss in The Battery?
Several consequences come with battery water loss. Below are some of them.
Low Capacity
The overall capacity of the battery will reduce when water is lost. Here is what happens, the active materials inside the cells of the battery will react only when they are well immersed inside the acid.
If the acid levels go low and the battery cells remain exposed, the active materials inside the battery that should react to produce power are also reduced.
What this means is that the battery will offer less power during recharge because the surface area to hold the charge is limited and this directly reduces the overall capacity of the battery.
Overheating
As we had said earlier, water is a very good conductor of heat this means that the water is capable of carrying the heat generated during electrochemical reactions and releasing it to the environment.
As the battery loses water, there is heat build-up inside the battery. When it reaches a point where the battery cannot withstand the heat anymore, thermal runaway kicks in and this will cause the electrodes and the plates to melt. When the battery gets to this stage it can explode or even cause fire.
Corrosion
We have talked about corrosion and mentioned that acid when not in the right concentration can lead to corrosion. Excess sulfuric acid will cause corrosion in the battery plates.
The concentration of sulfuric acid increases as water is lost. When the plates are corroded, the battery is left with less reaction materials and that implies a reduction in the battery capacity.
Oxidation of the Negative Electrode
The negative terminal is made of lead only. When water is lost from the battery, the negative terminal is exposed to oxygen and will react to form lead oxide. This will have the negative electrode destroyed or discharged.
How do I Prevent Water Loss in A Battery?
By managing the water loss in the battery, you will be able to prevent the battery from damage. Some of the measures you can take include:
Routine Watering of the Battery
Some batteries have a clear casing and it is easy to tell if the electrolyte level has dropped or is at the required level. When the levels drop, they need to be topped up to the required levels.
Only distilled water is used to top up the battery acid. NEVER should you add more acid into the electrolyte as it will raise the concentration of the electrolyte leaving the acid destroyed.
Tapped water or bottled water should not be used to top up the acid levels. This is because they contain minerals that can react with sulfuric acid to form sulfur compounds that will reduce the capacity of the battery.
Regulate Operational Temperature
Ventilation is very important when it comes to temperature regulation. The battery should be operated in an environment where excess heat can easily be lost in the environment
Handle Battery with Care
The battery should be handled with the proper care it needs. When the casing of the battery gets damaged the electrolyte can leak leading to water loss. It is advisable to always handle the battery carefully so that it gives you the service you deserve.
Conclusion
The electrolyte inside the battery is a very important component. You need to ensure that the right electrolyte levels are maintained. Always add distilled water to the acid to maintain the right levels.
NEVER add acid into the battery because then you will increase the acid concentration and corrosion is likely to kick in after that. Your battery can be permanently damaged due to this.