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.


Sulphuric Acid (H2SO4)

  • Skin contact: Immediately drench the affected area with clean water and remove any contaminated clothing. If any soreness or irritation persists seek medical advice.
  • Eye contact: Immediately wash out the eyes with clean water until initial burning subsides. Do not use eye drops but do seek prompt medical attention.
  • Ingestion: DO NOT induce vomiting but make patient drink as much water or milk as possible, followed by Milk of Magnesia, beaten eggs or vegetable oil and seek immediate medical attention.
  • Spillage: Small spillages can be quite simply dealt with by swilling away with plenty of water and neutralizing using Bicarbonate of Soda mixed with water (10 grams Bicarb to 1 litre of water)
  • Disposal: Suitably labeled, acid resistant containers should be used for transporting, neutralizing and disposal of Sulphuric acid.
  • Burns: Apply a dry sterile dressing and seek medical attention.

Safety Tips Sulphuric Acid

Sulphuric acid (H2SO4) is contained in batteries.

Battery acid is a poisonous and corrosive liquid, which will cause burns and irritation to the skin and eyes. Take precautions when charging as Sulphuric acid is given off in a fine mist.

  • Always handle batteries with care and keep upright.
  • Always charge in a well ventilated area.
  • Use eye protection and protective clothing where there is any risk of acid splashing or spillage.

Electrical Energy

Electrical energy can be supplied from batteries and charging equipment.

Burns may occur from the heating effect of tools and conductive objects in contact with live battery terminals or conductors. In addition, sparks and molten metal may be ejected and combustible materials, notably the gaseous fumes, ignited to cause potentially lethal explosions.

It is possible to receive a severe electric shock from charging equipment and from a number of batteries connected in series i.e. five or more 12 volt batteries (+60 volt nominal)

  • Before using conductive tools on a battery, remove metallic personal adornments from the hands and wrists.
  • Before working on a vehicle’s electrical system, blow across the terminals and the vent holes to disperse any fumes and disconnect the battery where there is any risk of accidental short circuits.
  • Always disconnect the earth terminal from a battery first and connect it last to prevent short circuiting.
  • Keep, charge, check and test batteries in a well ventilated area.
  • Do not place tools or conductive objects on top of batteries.
  • Before using a battery charger consult manufacturer’s literature.
  • Remember to switch the charger off before connecting or disconnecting a battery.

Emergency Procedure for Treating Electric Shocks

  • Electric Shock: Immediate action is essential in cases of severe electrical shock as the nerves controlling breathing and heart action may be affected. Do not delay treatment by calling for a doctor; this should be done quickly if help is available or when the casualty recovers.
  • Make sure it is safe to approach casualty. If the casualty is not clear of the electrical source, switch off the power. If this is not possible, attempt to separate the casualty from the conductor using a dry, insulating object (wood, rubber, brick, thickly folded newspaper, cardboard) and try to push or pull the casualty clear of contact. Do not touch casualty with bare hands.
  • Apply artificial respiration if necessary. Seek medical attention thereafter.
  • Explosion: Seek any necessary medical attention and remember that Sulphuric acid may have been ejected.

Emission of Gasses

Hydrogen and oxygen are emitted during charging and are emitted during cranking or movement of the battery.
An explosive atmosphere is created if the concentration of hydrogen in air exceeds 4%.

  • Keep, fill, charge, check and test batteries in a well ventilated area.
  • As an added precaution, blow air across the terminals and the vent holes to disperse any ignitable fumes.
  • Avoid sources of ignition close to batteries.
  • In particular:
  • No smoking.
  • No naked flames.
  • Switch off current before making or breaking electrical connection. Avoid sparks caused by accidental short circuits.
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