Thank you for your query on Healthcare Magic.
Eating non edible and non nutritive thing is called Pica
Although the tasting or mouthing objects is normal in infants and toddlers, pica after 2 years of life needs investigation.
But pica needs evaluation for lack of parenta nurturing including psychological and nutritional.
But keeping batteries in mouth is very dangerous as it may lead to corrosive injuries of food pipe due to alkali and lead toxication.
Screening should be done for lead intoxication, iron deficiency anemia
, and parasitic infestation and they should be treated accordingly if they present.
So I advise you to consult the Pediatrician
for the examination of deficiencies and screening for associated complications.
And keep batteires, medicines, chemicals out of reach of the child.