Honolulu motorists will no longer be able to phone in payments when parking at stalls equipped with the city’s "smart" meters.

But phone payments made up only 0.6 percent of all smart-meter transactions, so few motorists will feel the impact when the feature is suspended on Sept. 15, city Transportation Services Director Michael Formby said Thursday.

Credit card payments, however, still will be accepted at the 340 smart meters installed as a pilot project in May 2012.

About 9.4 percent of all payments received by the smart meters are from credit cards, or less than $10,000 a year, the city estimates. Ninety percent of motorists still do things the traditional way and drop coins into the meters.

Formby said the pay-by-phone function has been plagued by operational issues because significant battery power is required to transmit cellular data. Batteries that should have a three-year lifespan have been dying out in one year.

"They’re $30 a battery, so the cost of replacing the batteries for the pay-by-phone (option) exceeds the revenue, so we’re turning off the feature," he said.

New smart meters will be powered by small solar panels, he said.

The city also has received complaints from people who said the amount they paid did not reflect the time they received on the meter.

In Chinatown for a time, merchants were complaining that people who phoned in payments could do so throughout the day and would not move their vehicles, but the city has since reprogrammed the meters to disallow additional payments once a time limit is reached.

A sensor on the stall tracks movement and informs a corresponding meter if a new vehicle is in the stall, Formby said. The meter will then accept more payments and will reset the time on its clock so the next driver cannot inherit any time a previous motorist leaves on the meter.

The smart meters continue to be in a testing phase, he said.

The city may be ready to convert up to 2,400 parking stalls to smart meters in early 2014, Formby said.