There is often confusion when battery definitions are used to explain various aspects of the lead acid battery eg. sealed, maintenance free and other descriptive terms. The explanation of terms below is based on definitions contained in the IEC (60095-1 :2006) specification for lead acid starter batteries and is meant to provide clarity in terms of the various terms used to describe batteries.
Definition for vented (flooded) battery
This is the most common of automotive battery types. This type of battery has a cover with one or more openings through which gas generated by the battery may escape. A battery may also be fitted with tamper-proof plugs to prevent internal access to the battery but will still have an arrangement to allow gas generated by the battery to escape. The battery has “free” electrolyte which means that the acid moves freely within the battery.
Valve regulated (with gas recombination) battery
A secondary battery that is closed under normal conditions and has an arrangement that allows the escape of gas if the internal pressure exceeds a predetermined value.
The battery cannot normally receive an addition of water or electrolyte. In this type of battery, the electrolyte is immobilized. This means that the acid is held in either a gel or a glass mat structure.
Sealed battery
The valve regulated battery is often called a sealed battery because no addition of electrolyte or water is possible. However, the battery will have a pressure release vent to allow for the escape of gas generated by the battery.
Low water loss
Vented starter batteries may be designated as “low water loss” according to the IEC specification if the water loss of the battery is less than 4 grams per amp hour.
Very low water loss
Vented starter batteries may be designated as “very low water loss” according to the IEC specification if the water loss of the battery is less than one gram per amp hour.
Maintenance free
Some specifications use the term “maintenance free” to describe a battery that has a water loss below a certain level. The IEC specification does not use this term, but rather uses the terms low and very low water loss.
