Police in South Auckland are trying to identify who has been stealing hundreds of heavy truck batteries during night-time hours and illegally selling them.
In the last four months, more than 600 batteries were stolen from trucks and construction machinery in the district.
Lawnmowers and other garden tools were also being targeted.
The truck batteries, weighing as much as 30 kilograms, are worth up to $400 each.
Police patrols in the Wiri industrial area have been increased to try to reduce the burglaries.
The area prevention manager Inspector Bruce O'Brien said police were also working with scrap metal dealers to ensure the batteries are not being broken down and sold for scrap.