Auckland's trial of battery-powered buses is to step up next month, with one joining the airport route.

Two e-buses similar to those run in London have performed better than expected over seven months of service on the City Link loop through the CBD.

Auckland Transport said one would move to the 380 Airporter route between Manukau and the airport in December, and a third bus on loan from a manufacturer would join that route a month later.

"They are very reliable, customer feedback is very positive and on average they show costs only 25 per cent of a diesel, so those are very encouraging results," said Darek Koper, AT Metro's bus manager.

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Koper said over the past seven months the two e-buses had performed better than advertised, managing 259 kilometres on a day-long shift, using only 64 per cent of battery capacity.

He said they'd been told the buses would do up to 250 kilometres on a single charge.

"City Link is a very small circuit. The loads impact on consumption but the topography doesn't give us a true indication so we have to test those, as on other routes, well," he said.

The pair of trial buses cost $1.7 million and Koper hoped several more could be added with the assistance of operators or other manufacturers.

Auckland Mayor Phil Goff has previously called for no more fossil-fuelled buses being ordered after 2025, but told Stuff that could be brought forward.

"That was the date the C40 (global cities group) felt was practicable for making that change worldwide, so I relied on that," said Goff.

"Based on the trial process I hope they can bring forward their purchase of e-buses."

The first battery-powered electric bus took to the roads in this country in March as part of the shuttle service between AUT campuses in Auckland.

Wellington has begun the rollout of a fleet of double decker e-buses.

"We've set ourselves the target of [having] a 100 per cent electric bus fleet, and the first stop on our way is 10 new double-deckers this year, and 32 by 2021," Greater Wellington Regional Council chairman Chris Laidlaw said in July.

Christchurch's first battery-powered buses are due to arrive in March.

The regional council Environment Canterbury (ECan) plans to have an emmission-free bus fleet by 2030, but Christchurch City Council wants a transition to electric buses to start as soon as 2020.

In Auckland, the re-tendering of bus contracts over the past two years had seen a big investment in brand new diesel-powered buses, and one operator told Stuff the wisdom of that was questionable with both battery and hydrogen technology advancing quickly.

Goff said he hoped the roll-out of electric or hydrogen buses could happen more quickly in the city.

"Part with latest information on the Queen Street Valley that shows black carbon emissions are above safe levels, there's an imperative to do more, and more quickly," he said.