Maintenance-Free Batteries

Maintenance free battery is same like a regular lead acid battery. The chemistry of the battery is little bit change for sealed battery. The other difference is such kind of battery is sealed and there is no provision of addition of water in cells in sealed batteries. This kind of battery plates material is little different than the regular or conventional lead acid battery. This type battery plate grid contains calcium, strontium and cadmium to reduce gas formation during charging. In conventional lead acid batteries water electrolysis takes place and water molecules are broken down into Oxygen and Hydrogen molecules and the Hydrogen gas escape out from the battery vents. Whereas in the sealed lead acid battery the addition of the extra materials mentioned above reduces this gas formation during charging.

Sometimes additional support is provided to the plates which increases the conductivity of the plate to its connecting tab. The plates are wrapped on an envelope shape separator which covers the plate perfectly from all three sides. The separator is made of porous material and it gives path to the electrolyte but is seals the active materials effectively not to escape them from the battery plates. These batteries are sealed but small vent is provided on the top to the valve regulated chamber where water vapors are accumulated and regulated back to cells. This way water and gases cannot escape from the battery so there is no need to add additional water or distilled water periodically to maintain the electrolyte level like in conventional lead acid battery.

Maintenance free battery

Some maintenance free batteries have a built in hydrometer on the top of the battery case. That indicates the state of the charge of the battery. A hydrometer is an instrument which shows the specific gravity of the electrolyte in the battery. The specific gravity of the battery is directly proportional to the charge of the battery. The hydrometer on such batteries when they are charged more than 64% shows green indication. The black indication on the hydrometer shows partial charged battery less than 64% charges. Whereas a silver indication indicates that the battery electrolyte is completely used and become water and there is a need of battery replacement. This indication is an easy way for a driver to understand the battery condition and replacement interval.

Several battery manufacturers have changed the maintenance free batteries to another type low maintenance battery. For those batteries caps are removable for testing the electrolyte and to emulate the level of electrolyte.

There are a few advantages of sealed lead acid batteries:

1.       They have longer shelf life. Approximately 2 years.

2.       They have larger quantity of electrolyte in the battery compare to conventional batteries.

3.       These batteries are shipped with electrolyte in them and ready to use. There is no more need for bothering electrolyte refilling and charging when shipped.

4.       They have ability to provide more current even if the batteries are cold. They have higher cold cranking amperage.

5.       They have more resistance to overcharging. They withstand overcharging better than conventional batteries.

There are certain disadvantages also of the maintenance free batteries. These are:

1.       They have faster discharge rate on parasitic loads.

2.       They have low reserve capacity.

3.       They have a shorter life span. Their life is shorter than conventional lead acid batteries.

4.       They are not good on deep cycling.

These batteries are not suitable for high temperature exposure. At high temperature they become faulty due to grid growth.