While the batteries in quality toys sold by reputable retailers are usually secured safely,those in common household products are less secure. The danger is greatest in novelty items and inexpensive products like tea lights sold online and in discount stores. Very often the cheap gifts sold at schools'Father's Day sales run by Parents and Citizens'associations to raise funds can be dangerous.

Trent's mother Ms Macfadyen of North Rocks purged the house of batteries,including in calculators and remote controls. The source of the battery that Trent swallowed was a toy for an older child - not covered by the standard - that his eight year old brother Kobe had opened while experimenting to see if button batteries were magnetics.

When one gets stuck,it's"worse than acid",said Jared Brown,the director of the NSW Poisons Information Centre at Westmead Children's Hospital.

The 3 volt 20mm button batteries are often the worst,because they can contain a charge for as long as 10 years and they are big enough to lodge n a child's oesophagus. When they come in contact with body fluids,such as mucus or saliva in a nice warm environment,they create a circuit that releases a substance like caustic soda,which is a strong alkali that can burn through tissue.